Azure Keyvault and HMAC-SHA256 Pseudonymizer

In this article, using Azure Keyvault together with HMAC-SHA256.

Introduction to HMAC SHA-256

The HMAC-SHA256 is a SHA-256 cryptographic hashing function that combines SHA-256 with a secret key (that can be shared) to provide both data integrity (to ensure that data has not been altered) and data authenticity (that data originates from a sender that knows about the shared secret key of the HMAC-SHA256 hash). HMAC-SHA256 generates a Message Authentication Code (MAC)
that we can get both these benefits from, data authenticity and data integrity. Since it is 256 bits or 32 bytes, the hash can be represented as hexadecimal string of length 64. If it is represented as a base-64 string, it will be approximately 44 bytes long, given that a base-64 string will be padded in multiple of 4 characters.

Storing the shared secret key in Azure Keyvault

Azure Keyvault will be used to store the shared secret key. The secret key could be stored anywhere, but using a KeyVault in Azure makes it easier to keep it safe and apply rolling policies for the secret key. First off, to create an Azure Keyvault secret, make sure you have an Azure Keyvault created. Search for a resource called Key vaults with a key icon. Choose Create, enter a Key vault name and Region and resource group, Pay per use and Standard pricing tier. (Premium includes HSM backed keys, which will use dedicated physical devices - HSM = Hardware Security Module - for enhanced FIPS 140-2 Level 3 certified security). Once the keyvault is created, choose Object and Secrets. Click Generate/Import. Just enter a name for the secret and the secret value. It is suggested that they secret value you enter should be genereated from a cryptographically secure random generator and a length of at least 16 bytes and 32 bytes.

Generating a strong shared secret key for HMAC SHA-256

The following code can be used to generate a strong 256 (32-byte) key, and pasted into the Secret value

HmacSha256KeyGenerator.cs

using System.Security.Cryptography;

namespace MinimalApiSecurityExperimentsDotNet.Extensions
{

    public static class HmacSha256KeyGenerator
    {

        public static string GenerateStrongKey()
        {
            // Generate a 256-bit (32-byte) key
            byte[] key = new byte[32];
            using (var rng = RandomNumberGenerator.Create())
            {
                rng.GetBytes(key);
            }

            // Convert to Base64 for storage or display
            string base64Key = Convert.ToBase64String(key);
            return base64Key;
            //Console.WriteLine("Generated HMAC-SHA-256 Key (Base64):");
            //Console.WriteLine(base64Key);
        }

    }

}

MinimalApiSecurityDemo.csproj

The following Nuget packages can be added to work with Azure Keyvault secrets.

  <PackageReference Include="Azure.Identity" Version="1.14.2" />
  <PackageReference Include="Azure.Security.KeyVault.Keys" Version="4.8.0" />
  <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.8.0" />

Note that you do not need the Keys nuget package here if you only want to retrieve secrets. Azure KeyVault got three different object types - Keys, secrets and certificates. Only secrets will be looked at in this article.

KeyVaultSecretRetriever.cs

Let's look at key vault retrieval.

using Azure.Identity;
using Azure.Security.KeyVault.Secrets;

namespace MinimalApiSecurityExperimentsDotNet
{
    
    public class KeyVaultSecretRetriever
    {
        private readonly IConfiguration _configuration;
        public KeyVaultSecretRetriever(IConfiguration configuration)
        {
            _configuration = configuration;
        }

        public async Task<KeyVaultSecret>? GetSecretAsync(string secretName)
        {
            try
            {
                string keyVaultUri = _configuration["AzureKeyVault:VaultUri"] ?? throw new ArgumentNullException(nameof(keyVaultUri));
                var client = new SecretClient(new Uri(keyVaultUri), new DefaultAzureCredential());
                KeyVaultSecret secret = await client.GetSecretAsync(secretName);
                return secret;
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error retrieving the secret {secretName}: {ex.Message}");
                return null;
            }
        }     

    }

}

The SecretClient in the code above is the client used to retrieve the secret from Azure KeyVault. The client is from the Azure.Security.KeyVault.Secrets Nuget package. The DefaultAzureCredential used here means you will have to login in advance before retrieving the secret. There are different credential types you can use instead, but this default credential type is the easiest to use for testing out. If you run the code above from the console, you can for example install the Azure Powershell module and run az login. The following appsettings file can be used for the code above.

appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",

  "AzureKeyVault": {
    "VaultUri": "https://yourkeyvaultsomewhereinazure.vault.azure.net/",
    "HmacSha256SecretName":  "YourExampleHmacStrongKey"
  }

}

Pseudonymizer class

The following pseudonymizer class uses HMAC-SHA256 to generate a pseudonym for a given message. This can be used for generating a value for sensitive data with a key. The key can be shared between sender and receiver to avoid exposing sensitive values in clear text.

Pseudonymizer.cs

using System.Text;

namespace MinimalApiSecurityExperimentsDotNet
{

    public class Pseudonymizer
    {
        private readonly byte[]? _key;

        public Pseudonymizer(string key)
        {
            if (!string.IsNullOrWhiteSpace(key))
            {
                _key = Encoding.UTF8.GetBytes(key);
            }
        }

        /// <summary>
        /// Outputs a pseudonymized version of the input string using HMAC SHA256.       
        /// </summary>
        /// <param name="message"></param>
        /// <param name="outputToHexString">Output to hex string if true. If false, base-64 string is returned</param>
        /// <returns></returns>
        public string? Pseudonymize(string? message, bool outputToHexString = true)
        {
            if (string.IsNullOrWhiteSpace(message) || _key == null)
            {
                return message;
            }
            using var hmac = new System.Security.Cryptography.HMACSHA256(_key);
            var hash = hmac.ComputeHash(Encoding.UTF8.GetBytes(message));
            return outputToHexString ? Convert.ToHexString(hash) : Convert.ToBase64String(hash);
        }

        public bool Verify(string input, string pseudonym)
        {
            if (string.IsNullOrEmpty(input) || string.IsNullOrEmpty(pseudonym))
            {
                return false;
            }
            var computedPseudonym = Pseudonymize(input);
            return computedPseudonym == pseudonym;
        }

    }

}

The code above shows that we can both psedonymize and verify the pseudonym. Next up, a provider for creating an instance of this Pseudonymizer for use in ASP.net Core, for example.

PseudonymizerProvider.cs

namespace MinimalApiSecurityExperimentsDotNet.Extensions
{

    public class PseudonymizerProvider
    {

        private Pseudonymizer? _pseudonymizer;

        public void Set(Pseudonymizer pseudonymizer)
        {
            _pseudonymizer = pseudonymizer;
        }

        public Pseudonymizer Get()
        {
            return _pseudonymizer ?? throw new InvalidOperationException("Pseudonymizer not initalized");
        }

    }

}

The following Hosted service sets up the pseudonymizer service. It will start up when the Asp.net core application is starting, however after the DI container has been built.

PseudonymizerHostedService .cs

using Azure.Security.KeyVault.Secrets;

namespace MinimalApiSecurityExperimentsDotNet.Extensions
{

    public class PseudonymizerHostedService : IHostedService
    {

        private readonly IServiceProvider _provider;

        public PseudonymizerHostedService(IServiceProvider provider)
        {
            _provider = provider;
        }

        public async Task StartAsync(CancellationToken cancellationToken)
        {
            using var scope = _provider.CreateScope();
            var config = scope.ServiceProvider.GetRequiredService<IConfiguration>();
            var keyVaultRetriever = new KeyVaultSecretRetriever(config);
            var hmacSha256SecretName = config["AzureKeyVault:HmacSha256SecretName"];
            if (hmacSha256SecretName == null)
            {
                throw new InvalidOperationException($"Config '{hmacSha256SecretName}' not is missing.");
            }
            KeyVaultSecret? secret = await keyVaultRetriever.GetSecretAsync(hmacSha256SecretName);

            if (secret == null)
            {
                throw new InvalidOperationException($"Secret '{hmacSha256SecretName}' not found in Key Vault.");
            }

            var pseudonymizer = new Pseudonymizer(secret.Value);

            // Register the pseudonymizer in the pseudonymizerProvider
            var pseudonymizerProvider = scope.ServiceProvider.GetRequiredService<PseudonymizerProvider>();
            pseudonymizerProvider.Set(pseudonymizer);
        }

        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    }

}

In the Program.cs of a sample Asp.net Web API with minimal API, the provider and the hosted service is registered before building the webapplication with .Build().

Program.cs

using MinimalApiSecurityExperimentsDotNet.Extensions;

namespace MinimalApiSecurityExperimentsDotNet
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.

            builder.Services.AddControllers();

            // Add Swagger services
            builder.Services.AddSwaggerGen();
            builder.Services.AddEndpointsApiExplorer();

            // Adding keyvault access via registering PseudonymizerHostedService 
            builder.Services.AddSingleton<PseudonymizerProvider>();
            builder.Services.AddHostedService<PseudonymizerHostedService>();

            var app = builder.Build();

            // Configure the HTTP request pipeline.

            app.UseHttpsRedirection();

            app.UseAuthorization();

            app.MapControllers();

            // Enable Swagger middleware 
            if (app.Environment.IsDevelopment())
            {
                app.UseSwagger();
                app.UseSwaggerUI();
            }
          
            app.MapGet("/generatestrongkey", () =>
            {
                return HmacSha256KeyGenerator.GenerateStrongKey();

            });

            app.MapGet("/pseudonymize", (string? key, string? value) =>
            {
                var pseudonym = new Pseudonymizer(key).Pseudonymize(value, outputToHexString: true);
                return Results.Json(pseudonym);
            });

            app.MapGet("/pseudonymize/verify", (string? key, string? value, string? pseudonym) =>
            {
                var pseudonymizer = new Pseudonymizer(key);
                var isValid = pseudonymizer.Verify(value, pseudonym);
                return Results.Json(isValid);
            });

            //Example using the injected singleton PseudonymizerProvider

            app.MapGet("/pseudo", (string? input, PseudonymizerProvider pseudonymizerProvider) =>
            {
                var pseudonymizer = pseudonymizerProvider.Get();
                var result = pseudonymizer.Pseudonymize(input); //pseudonymize the input using the inject Pseudonymizer instance. This will use HMAC SHA256 under the hood.
                return Results.Ok(new { message = input, pseudonym = result });
            });

            app.MapGet("/getkeyvaultsecret", async (string secretName) =>
            {
                var keyvaultRetriever = new KeyVaultSecretRetriever(builder.Configuration);
                var secret = await keyvaultRetriever.GetSecretAsync(secretName);
                return Results.Json(secret);
            });          

            app.Run(); 
        }
    }


}

The benefits of registering the pseudonymizer's hosted service and provider in the container is shown in the code above. We can easily pseudonymize and use Azure Key vault stored secret for the HMAC-SHA256 hash / pseudonoym.

 //Example using the injected singleton PseudonymizerProvider

app.MapGet("/pseudo", (string? input, PseudonymizerProvider pseudonymizerProvider) =>
{
    var pseudonymizer = pseudonymizerProvider.Get();
    var result = pseudonymizer.Pseudonymize(input); //pseudonymize the input using the inject Pseudonymizer instance. This will use HMAC SHA256 under the hood.
    return Results.Ok(new { message = input, pseudonym = result });
});

Summary

The pseudonymizer is initialized and registered as a singleton, it got a dependency against Azure Keyvault service at startup, but further on pseudonymizing can now use the singleton instance of the pseudonymizer that is registered by the hosted service at application startup. The pseudonymizer can for example pseudonymize sensitive values and hide their content. A receiver can be shown this pseudonymized value in the response. There pseudonymized value could also be described as for example one of these three descriptions:

• Key identifier / alias
• Obfuscated key named
• Derived key label

If the receiver got the shared secret key, since it is a one-way cryptographic algorithm, obtaining the original value is still only possible via a brute-force dictionary attack. However, it can be used for example as a pseudo-id that is shared and also identify for example a shared identifier, for example a patient identifier for multiple registered documents in a database for example. The pseudo id can be even stored in the database as a way of obfuscating sensitive values such a SSN / PID (Patient Id, SSN = Social Security Number).

Note about Keyvault access

Just because you know the url to an Azure keyvault and possible the secret's name, does of course not mean you got access to the secret. Inside the Azure Keyvault, clik on Access Control (IAM) to get started. To just test things out, follow the guide by clicking the button Add role assignment. Follow the wizard to gain access to your key vault. Search for role Key Vault Administrator. Click Next. Choose Select members to choose for example your own user. Click Next Click Review and assign. Finally you have added access to your Key vault. This must be done even for the Key vault you have created yourself. Of course, if you use Azure AD, you can choose different members here and authorize fine-grained access.

Object detection with Machine Learning

In this article, a demo performing object detection in images using machine learning is presented. ML.net will be used for the machine training in the Blazor serverside app the demo is made with. The demo will describe how you can train a machine learning model to detect stop signs in United States from some 50 images, downloaded from Unsplash website. You can of course choose whatever object to detect here and obtain sample images from for example sites such as Unsplash. There are no official lower limit on the needed images you need for reliable detection of objects in images using machine learning. Obviously, your images should include viewing the object from different angles and being partly obscured and similar variations, such as weathering effects (snow et cetera) and different lighting conditions (day, night, dusk, dawn and so on). High quality object detection will use thousands of images for training and use powerful GPUs in the cloud. I have trained the learning model on my own PC using a CPU. It took 830 seconds, some 13 minutes in all. ML.net supports computing machine learning models in the clouds, some cost may of course be expected instead of running in on cheaper hardware such as your own PC (CPU). The benefit of using GPUs in the cloud is that the machine learning model can use more diffusion models and compare which machine learning model is optimal. This demands a lot of computing. Note that the Modelbuilder of ML.net is used in VS 2022. This is available after installing the ML.net workload in VS 2022. I have also used VoTT to tag the 50+ images I used for training set. I have added the source code in my Github repo here:

https://github.com/toreaurstadboss/ObjectDetectionMachineLearning

VOTT - Visual Object Tagging Tool

ML.net object detection uses input from VoTT tool where a human (you!) has tagged the object(s) of interest in the image. Note that a stopsign along a road or street can be multiple places in an image. Some places for example, we see an object 2-3 times of course. Your objective in doing a good interpretation in training data (pictures!) of tagging and labelling objects of interest in Vott is a straight forward process. VoTT is available for download here, click in the releases of the Github repo to find latest stable installer (exe):


https://github.com/microsoft/VoTT/releases/tag/v2.2.0


https://github.com/microsoft/VoTT Vott repo on Github
Here is a screenshot of Vott while I am tagging pictures : You can open a folder with several pictures, I am using .png format, and then use the polygon tool to 'lasso around' the contours of each object of interest in the image. A label must be designated also. This process is manually repeated. A minimum of about 50 images such be considered, but a reliable trained machine learning model in productions should probably be trained with a lot more, in the several thousands. However, in the beginning, it would be benificial to keep the count of images low so finding the optimum machine learning algorithm is easier without such a large training set. In Ml.net, the algorithm ObjectDetectionMulti won, however also only one model was explored. Using GPUs in the cloud would at least reduce computation time and yield higher quality diffusion models.

Screenshot of the demo

The following screenshot shows three detected objects in the test image. The machine learned model is trained to detect Stop signs, used in road signs of roads and streets in United States. Interestingly, the machine learning model also detected the stop sign poining the other way for meeting traffic, so a total of three stop signs were detected in the rail road crossing sample image. The fourth stop sign was not detected, however, I have trained the data not on road signs rotated away from camera. Training also to detect stop signs in these cases would perfect this even better. But I am quite pleased with the results when I test out the machine learned model.

First, let's look at the code behind the demo shown in the screenshot above.

Machine learning model exposed via Web API

Using ML.net we can not only train a machine learning models to detect object in images, we can also via using ML.net generate the API that will process images and returns objects found in images, if any. ML.net object detection supports images of format .png, .jpeg and .bmp. In the demo, .png images were used. Actually the demo used high-res images from the web site Unsplash, which provides beautiful and royalty free of use images to use with for example meachine learning.

The API and endpoint for the processing of images is shown next. The client specifies the file name of the image to analyse and after processing, the resulted detected objects are returned. If any objects were found, we will get these objects in summary format of bounding boxes and detected labels from the machine learned model. ML.Net generated the Web api code here. Note that the POST endpoint was made manually by myself. We turn off caching here through response headers and note that the bounding box coordinates are returned scaled to a 800x600 virtual image. The bounding boxes are returned as quadruples (four floats per object) in the float array returned. The POST endpoing in the minimal API shown below shows how these bounding boxes are calculated and returned. I have not refactored this code yet into a helper method, but you can use this code as a reference to how to rescale the calculated bounding boxes from the virtual 800x600 image back to the original image pixel width and height.

Program.cs | StopsignDetection_webapi1 project

<!-- This file was auto-generated by ML.NET Model Builder. -->
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.ML;
using Microsoft.OpenApi.Models;
using Microsoft.ML.Data;
using System.Drawing;
using System.IO;
using System.Threading.Tasks;
using StopSignDetection_WebApi1;
using Microsoft.AspNetCore.Mvc;

<!-- Configure app -->
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddPredictionEnginePool<StopSignDetection.ModelInput, StopSignDetection.ModelOutput>()
    .FromFile("StopSignDetection.mlnet");

builder.Services.AddEndpointsApiExplorer();

builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new OpenApiInfo { Title = "Object detection - Stop sign detection", Description = "Docs for my API", Version = "v1" });
});
var app = builder.Build();

app.UseSwagger();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "Object detection - Machine learning MLN.");
    });
}

<!-- Define prediction route & handler -->
app.MapPost("/predict",
    async (HttpContext context, PredictionEnginePool<StopSignDetection.ModelInput, StopSignDetection.ModelOutput> predictionEnginePool, [FromBody] PredictRequest request) =>
    {
        context.Response.Headers["Cache-Control"] = "no-store, no-cache, must-revalidate, max-age=0";
        context.Response.Headers["Pragma"] = "no-cache";
        context.Response.Headers["Expires"] = "0";

        var image = MLImage.CreateFromFile(request.ImagePath);

        var input = new StopSignDetection.ModelInput()
        {
            Image = image,
        };

        int originalWidth = image.Width;
        int originalHeight = image.Height;

        const int virtualWidth = 800;
        const int virtualHeight = 600;

        var prediction = predictionEnginePool.Predict(input);
        var boxes = prediction.PredictedBoundingBoxes;

        for (int i = 0; i < boxes.Length; i += 4)
        {
            float left = boxes[i];
            float top = boxes[i + 1];
            float width = boxes[i + 2];
            float height = boxes[i + 3];

            float scaledLeft = left * originalWidth / virtualWidth;
            float scaledTop = top * originalHeight / virtualHeight;
            float scaledWidth = width * originalWidth / virtualWidth;
            float scaledHeight = height * originalHeight / virtualHeight;

            Console.WriteLine($"Box {i / 4}: X={scaledLeft}, Y={scaledTop}, Width={scaledWidth}, Height={scaledHeight}");

            (boxes[i], boxes[i + 1], boxes[i + 2], boxes[i + 3]) = (scaledLeft, scaledTop, scaledWidth, scaledHeight);  //assign using tuples and update the float array per object
        }

        return await Task.FromResult(prediction);
    });

app.Run();

PredictRequest is a simple class using as the request object while POST-ing.

PredictRequest.cs | StopsignDetection_webapi1 project

namespace StopSignDetection_WebApi1 { public class PredictRequest { public string ImagePath { get; set; } = string.Empty; } }

Over to the client, which is a Blazor serverside. The following UI is in the component that shows the UI with code-behind.

Home.razor

@page "/"
@using Microsoft.AspNetCore.Components.Forms

<PageTitle>Home</PageTitle>

<h1>Object detection using Machine learning</h1>

<script src="js/home.js" type="text/javascript"></script>

<p>
    Upload an image to use the Object detection demo. The machine-learned ML.Net model will detect <em>Stop signs</em> and
    display bounding boxes around each stop sign in the image. The stop sign is trained to use those used as traffic signs in United States
    along streets and roads.
</p>

<div class="container">

    <div class="row align-items-start">
        <div class="col">
            <label><b>Select a picture to run stop sign object detection</b></label><br />
            <InputFile OnChange="@OnInputFile" accept=".jpeg,.jpg,.png" />
            <br />
            <code class="alert-secondary">Supported file formats: .jpeg, .jpg and .png. (.bmp also supported) Max image file upload size : 10 MB</code>
            <br />
        </div>
    </div>

    <div class="row align-items-start">
        <div class="col">
            <label><b>Detected objects (stop-signs) in the loaded image:</b></label><br />

            @if (LatestPrediction?.predictedLabel?.Count > 0)
            {
                <table class="table table-bordered table-striped table-hover mt-3">
                    <thead class="table-dark">
                        <tr>
                            <th>#</th>
                            <th>Label</th>
                            <th>X1</th>
                            <th>Y1</th>
                            <th>X2</th>
                            <th>Y2</th>
                            <th>Confidence</th>
                        </tr>
                    </thead>
                    <tbody>
                        @for (int i = 0; i < LatestPrediction.predictedLabel.Count; i++)
                        {
                            var label = LatestPrediction.predictedLabel.ElementAt(i);
                            var bbox = LatestPrediction.predictedBoundingBoxes.Skip(i * 4).Take(4).ToArray();
                            var score = LatestPrediction.score.ElementAt(i);

                            <tr>
                                <td>@(i + 1)</td>
                                <td>@label</td>
                                <td>@bbox[0].ToString("0.00")</td>
                                <td>@bbox[1].ToString("0.00")</td>
                                <td>@bbox[2].ToString("0.00")</td>
                                <td>@bbox[3].ToString("0.00")</td>
                                <td>@score.ToString("0.0000")</td>
                            </tr>
                        }
                    </tbody>
                </table>
            }
            else
            {
                <p class="text-muted">No predictions available.</p>
            }
        </div>
    </div>

    <div class="row align-items-start">
        <div class="col overflow-scroll">
            <label class="alert-info">Preview of the selected image</label>
            <div>
                <img id="PreviewImage" style="border:1px solid black;" src="@UploadedImagePreview" /><br />
            </div>
        </div>
        <div class="col overflow-scroll">
            <label class="alert-info">Image with bounding boxes</label>
            <canvas height="400" id="PreviewImageBbox" style="border:solid 1px black">
            </canvas>
            <br />
        </div>
    </div>

</div>

The image you want to analyze is uploaded using an InputFile component in Blazor. This uses HTML file upload control. After file is uploaded, the API will be called in the event handler OnInputFile. The code behind of the home component is shown next.

Home.razor.cs

using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Forms;
using Microsoft.JSInterop;
using ObjectDetectionMachineLearning.Web.Models;
using System.Text;
using System.Text.Json;

namespace ObjectDetectionMachineLearning.Web.Components.Pages
{
    partial class Home
    {

        [Inject]
        private HttpClient Http { get; set; } = default!;

        [Inject]
        private IJSRuntime JsRunTime { get; set; } = default!;

        private string? UploadedImagePreview;

        private MLPrediction LatestPrediction = default!;

        /// <summary>
        /// Uploads an image and sets the imagePreview property to display it
        /// </summary>
        /// <param name="e"></param>
        /// <returns></returns>

        private async Task OnInputFile(InputFileChangeEventArgs e)
        {
            var file = e.File;

            if (file != null && (file.ContentType == "image/jpeg" || file.ContentType == "image/png"))
            {
                string savedUploadedImageFullPath = await SaveUploadedImage(file);

                // Optional: Set preview if you still want to show it in the UI
                using var ms = new MemoryStream();
                using var previewStream = file.OpenReadStream(maxAllowedSize: 10 * 1024 * 1024);
                await previewStream.CopyToAsync(ms);
                var bytes = ms.ToArray();
                UploadedImagePreview = $"data:{file.ContentType};base64,{Convert.ToBase64String(bytes)}";

                string? prediction = await CallPredictApiAsync(savedUploadedImageFullPath);

                var jsonBboxes = CreateBoundingBoxJson(prediction);
                await JsRunTime.InvokeVoidAsync("InitLoadBoundingBoxes", jsonBboxes);

                Console.WriteLine($"Prediction {prediction}");

                //StateHasChanged();
            }
        }

        private string CreateBoundingBoxJson(string? prediction)
        {
            if (string.IsNullOrEmpty(prediction))
                return "[]";
            try
            {
                var mlPrediction = JsonSerializer.Deserialize<MLPrediction>(prediction);
                LatestPrediction = mlPrediction;
                return ConvertMLPredictionToBoundingBoxJson(mlPrediction!);
            }
            catch (JsonException ex)
            {
                Console.WriteLine($"Error deserializing prediction: {ex.Message}");
                return "[]";
            }

        }

        public static string ConvertMLPredictionToBoundingBoxJson(MLPrediction prediction)
        {
            var boxes = prediction.predictedBoundingBoxes;
            var labels = prediction.predictedLabel ?? new List<string>();
            var scores = prediction.score ?? new List<float>();

            if (boxes == null || boxes.Count % 4 != 0)
                return "[]";

            var results = new List<object>();

            for (int i = 0; i < boxes.Count; i += 4)
            {
                float x1 = boxes[i];
                float y1 = boxes[i + 1];
                float x2 = boxes[i + 2];
                float y2 = boxes[i + 3];

                float width = x2 - x1;
                float height = y2 - y1;

                results.Add(new
                {
                    Name = i / 4 < labels.Count ? labels[i / 4] : "Unknown",
                    X = x1,
                    Y = y1,
                    Width = width,
                    Height = height,
                    Confidence = i / 4 < scores.Count ? scores[i / 4].ToString("0.0000") : "0.0000"
                });
            }

            return JsonSerializer.Serialize(results, new JsonSerializerOptions { WriteIndented = true });
        }

        private static async Task<string> SaveUploadedImage(IBrowserFile file)
        {
            var uploadsFolder = Path.Combine(Environment.CurrentDirectory, "UploadedImages");
            Directory.CreateDirectory(uploadsFolder); // Ensure folder exists

            var fileName = $"{Guid.NewGuid()}_{file.Name}";
            var filePath = Path.Combine(uploadsFolder, fileName);

            using (var stream = file.OpenReadStream(maxAllowedSize: 10 * 1024 * 1024))
            using (var fileStream = new FileStream(filePath, FileMode.Create))
            {
                await stream.CopyToAsync(fileStream);
            }

            return filePath;
        }

        private async Task<string?> CallPredictApiAsync(string imagePath)
        {
            try
            {
                var payload = new { imagePath = imagePath };
                var content = new StringContent(JsonSerializer.Serialize(payload), Encoding.UTF8, "application/json");

                var response = await Http.PostAsync("https://localhost:65194/predict", content);

                if (response.IsSuccessStatusCode)
                {
                    var result = await response.Content.ReadAsStringAsync();
                    Console.WriteLine("Prediction result: " + result);
                    return result;
                }
                else
                {
                    Console.WriteLine($"API call failed: {response.StatusCode}");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error calling API: " + ex.Message);
            }

            return null;
        }

    }
}

home.js

Over to the client side javascript next, which handles the loading of bounding boxes using Canvas in HTML5.

<script type="text/javascript">
var colorPalette = [
    "red", "yellow", "blue", "green", "fuchsia",
    "moccasin", "purple", "magenta", "aliceblue",
    "lightyellow", "lightgreen"
];

function rescaleCanvas() {
    var img = document.getElementById('PreviewImage');
    var canvas = document.getElementById('PreviewImageBbox');
    var displayWidth = img.clientWidth;
    var displayHeight = img.clientHeight;
    canvas.width = displayWidth;
    canvas.height = displayHeight;
}

function LoadBoundingBoxes(objectDescriptions) {
    if (!objectDescriptions) {
        alert('No objects found in image.');
        return;
    }

    console.log(new Date() + ' ' + 'home.js : Loading bounding boxes from returned results ..');

    var objectDesc = typeof objectDescriptions === "string"
        ? JSON.parse(objectDescriptions)
        : objectDescriptions;

    var canvas = document.getElementById('PreviewImageBbox');
    var img = document.getElementById('PreviewImage');
    var ctx = canvas.getContext('2d');

    var scaleX = canvas.width / img.naturalWidth;
    var scaleY = canvas.height / img.naturalHeight;

    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
    ctx.font = "10px Verdana";

    console.log(`ctx.drawImage Canvas width: ${canvas.width} Canvas height: ${canvas.height} ScaleX ${scaleX} ScaleY ${scaleY}`);

    for (var i = 0; i < objectDesc.length; i++) {
        const obj = objectDesc[i];
        const x = obj.X * scaleX;
        const y = obj.Y * scaleY;
        const width = obj.Width * scaleX;
        const height = obj.Height * scaleY;

        ctx.beginPath();
        ctx.strokeStyle = "black";
        ctx.lineWidth = 1;
        ctx.fillText(obj.Name, x + width / 2, y + height / 2);
        ctx.fillText("Confidence: " + obj.Confidence, x + width / 2, 10 + y + height / 2);
    }

    for (var i = 0; i < objectDesc.length; i++) {
        const obj = objectDesc[i];
        const x = obj.X * scaleX;
        const y = obj.Y * scaleY;
        const width = obj.Width * scaleX;
        const height = obj.Height * scaleY;

        ctx.fillStyle = getColor();
        ctx.globalAlpha = 0.2;
        ctx.fillRect(x, y, width, height);

        ctx.globalAlpha = 1.0;
        ctx.lineWidth = 3;
        ctx.strokeStyle = "blue";
        ctx.strokeRect(x, y, width, height);

        ctx.fillStyle = "black";
        ctx.fillText("Color: " + getColor(), x + width / 2, 20 + y + height / 2);
    }

    console.log('Bounding boxes:', objectDesc);
}

function getColor() {
    var colorIndex = Math.floor(Math.random() * colorPalette.length);
    return colorPalette[colorIndex];
}

function InitLoadBoundingBoxes(objectDescriptions) {
    const img = document.getElementById('PreviewImage');

    const draw = () => {
        setTimeout(() => {
            LoadBoundingBoxes(objectDescriptions);
        }, 1000);
    };

    if (!img.complete) {
        img.onload = draw;
    } else {
        draw();
    }
}
</script>

ML.net project for Object detection

The repo also contains a project with the Object detection with the training data. You will need the ML.net workload here to work ML.Net in VS 2022.

Model builder in VS 2022

Training with pictures - training data

The ML.net project allows you to via the built-in ModelBuilder UI select the pictures that you can train the machine learning model.

Concluding notes

We have seen how we fairly conveniently can train a machine learning model to analyze images and detect objects. In this demo, stop signs along roads and streets in United States is used for the training. Note that you with using Vott, the Visual Object Tagging Tool, you can enter multiple labels. i.e. you can train the machine learning model to detect and interpret multiple types of objects. For example speed signs and stop signs to take an example. A self-driving car would use machine learning to intelligently interpret in real time such road signs and use additional input such as GPS, road databases and LIDAR to ultimately achieve a situation awareness that is needed to drive a car. Of course, we have just trained a machine learning model to just detect stop signs from 50 training images, but now you should have a better understanding how you can train machine learning models to detect objects in images.

Blazorise Datepicker with highlighting of dates

The Blazorise Datepicker is a date picker control for setting dates in Blazor WASM web assembly apps. It uses Flatpickr to provide a user friendly UI for selecting a date and navigate among months and years. It is used in web apps that use Blazor. The date picker is documented here :
https://blazorise.com/docs/components/date-picker
This date picker does not support highlighting certain dates. It do support enabling specified dates or disabling specified dates. But highlighting dates is not possible. I have added a Github repo where this is added support for :

https://github.com/toreaurstadboss/BlazoriseDatePickerWithHolidays

First off, the following custom Blazor component provides the custom date picker with the support for highlighting specified dates.

CustomDatePicker.razor

@using Blazorise
@using Blazorise.Localization
@using BlazoriseDatePickerWithHolidays.Service
@using System.Globalization
@using static BlazoriseDatePickerWithHolidays.Service.HolidayService
@inject IJSRuntime JS
@inject ITextLocalizerService TextLocalizerService

<Addons>
    <Addon AddonType="AddonType.Body">
        <DatePicker TValue="DateTime"
                    Date="@SelectedDate"
                    FirstDayOfWeek="@FirstDayOfWeek"
                    DateChanged="@OnDateChanged"
                    InputFormat="@InputFormat"   
                    InputMode="@InputMode"
                    DisplayFormat="@DisplayFormat"                    
                    Placeholder="@Placeholder"
                    TimeAs24hr="@TimeAs24hr"
                    @attributes="@AdditionalAttributes"
                    @ref="datePicker" />
    </Addon>
    <Addon AddonType="AddonType.End">
        <Button Class="addon-margin" Color="Color.Primary" Clicked="@(() => datePicker?.ToggleAsync())">
            <Icon Name="IconName.CalendarDay" />
        </Button>
    </Addon>
</Addons>

@code {
    /// <summary>
    /// List of dates to be highlighted in the date picker. Each date can have an annotation (e.g., holiday name) that will be shown as a tooltip.
    /// </summary>
    [Parameter]
    [EditorRequired]
    public List<AnnotatedDateTime> HighlightedDays { get; set; }

    /// <summary>
    /// The CSS class to apply to highlighted dates in the calendar.
    /// </summary>
    [Parameter]
    public string HighlightCssClass { get; set; } = "pink-day"; //Default CSS class pink-day is a custom CSS class defined in wwwroot/css/app.css

    /// <summary>
    /// The first day of the week in the date picker calendar. Defaults to Monday.
    /// </summary>
    [Parameter]
    public DayOfWeek FirstDayOfWeek { get; set; } = DayOfWeek.Monday;

    /// <summary>
    /// Whether to display time in 24-hour format. Defaults to true.
    /// </summary>
    [Parameter]
    public bool TimeAs24hr { get; set; } = true;

    /// <summary>   
    /// The locale to use for the date picker, which affects date formatting and localization. 
    /// Supported locales : https://blazorise.com/docs/helpers/localization
    /// </summary>
    [Parameter]
    public string Locale { get; set; } = "en-US";

    /// <summary>
    /// The input mode for the date picker, which can be either Date or DateTime or Month.
    /// </summary>
    [Parameter]
    public DateInputMode InputMode { get; set; } = DateInputMode.Date;

    /// <summary>
    /// The currently selected date in the date picker.
    /// </summary>
    [Parameter] 
    public DateTime SelectedDate { get; set; }

    /// <summary>
    /// Event callback triggered when the selected date changes.
    /// </summary>
    [Parameter] 
    public EventCallback<DateTime> SelectedDateChanged { get; set; }

    /// <summary>
    /// The input format string for displaying the date in the input field.
    /// </summary>
    [Parameter] 
    public string? InputFormat { get; set; } = "dd.MM.yyyy";

    /// <summary>
    /// The display format string for showing the date in the calendar.
    /// </summary>
    [Parameter] 
    public string? DisplayFormat { get; set; } = "dd.MM.yyyy";

    /// <summary>
    /// Placeholder text to display when no date is selected.
    /// </summary>
    [Parameter] 
    public string? Placeholder { get; set; }

    /// <summary>
    /// Whether to show the clear button in the date picker.
    /// </summary>
    [Parameter] 
    public bool ShowClearButton { get; set; } = true;

    /// <summary>
    /// Additional attributes to be splatted onto the underlying DatePicker component.
    /// </summary>
    [Parameter(CaptureUnmatchedValues = true)] 
    public Dictionary<string, object>? AdditionalAttributes { get; set; }

    /// <summary>
    /// Handles component rendering and registers JS interop for month and year changes.
    /// </summary>
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            _dotNetRef = DotNetObjectReference.Create(this);
            await JS.InvokeVoidAsync("registerFlatpickrMonthChange", "input.flatpickr-input", _dotNetRef);
            await JS.InvokeVoidAsync("registerFlatpickrYearChange", "input.flatpickr-input", _dotNetRef);
        }
        await ReloadDatesToHighlight();
    }

    protected override void OnParametersSet()
    {
        if (Locale != null){
            TextLocalizerService.ChangeLanguage(Locale);
        }
    }

    /// <summary>
    /// Invoked from JS when the month is changed in the calendar.
    /// </summary>
    [JSInvokable]
    public async Task OnMonthChanged()
    {
        await ReloadDatesToHighlight();
    }

    /// <summary>
    /// Invoked from JS when the year is changed in the calendar.
    /// </summary>
    [JSInvokable]
    public async Task OnYearChanged()
    {
        await ReloadDatesToHighlight();
    }

    /// <summary>
    /// Disposes JS interop references and the DatePicker component.
    /// </summary>
    public async ValueTask DisposeAsync()
    {
        _dotNetRef?.Dispose();
        if (datePicker != null)
            await datePicker.DisposeAsync();
    }
    
    /// <summary>
    /// Highlights the specified dates in the calendar using JS interop.
    /// </summary>
    private async Task ReloadDatesToHighlight()
    {
        if (HighlightedDays == null)
            return;

        string chosenLocale = this.Locale ?? "en-US";

        //Console.WriteLine("chosenLocale:" + chosenLocale);

        var datesToHighlight = HighlightedDays
            .Select(d => new { annotation = d.Annotation, date = d.Value.ToString("MMMM d, yyyy", new CultureInfo(chosenLocale)) })
            .ToArray();

        //Console.WriteLine(System.Text.Json.JsonSerializer.Serialize(datesToHighlight));

        await JS.InvokeVoidAsync(
            "highlightFlatpickrDates",
            ".flatpickr-calendar",
            datesToHighlight,
            HighlightCssClass // Pass the class as an extra argument
        );
    }

    /// <summary>
    /// Optionally provides a CSS class for a given date. Not used in this implementation.
    /// </summary>
    private string GetDateClass(DateTime date)
    {
        return string.Empty;
    }

    /// <summary>
    /// Handles the date change event from the DatePicker and propagates it to the parent component.
    /// </summary>
    private async Task OnDateChanged(DateTime newValue)
    {
        SelectedDate = newValue;
        await SelectedDateChanged.InvokeAsync(newValue);
    }

    private DatePicker<DateTime>? datePicker;
    private DotNetObjectReference<CustomDatePicker>? _dotNetRef;
}

Notice the trick done to capture unmatched values in case some parameters of DatePicker in the custom date picker is missing and we still want the user of this component to set a parameter of the date picker component :

    /// 

    /// Additional attributes to be splatted onto the underlying DatePicker component.
    /// 
    [Parameter(CaptureUnmatchedValues = true)] 
    public Dictionary<string, object>? AdditionalAttributes { get; set; }

The calls to IJSRunTime to register callback script handlers will register callbacks for the component, this is done in this line :

_dotNetRef = DotNetObjectReference.Create(this);
await JS.InvokeVoidAsync("registerFlatpickrMonthChange", "input.flatpickr-input", _dotNetRef); 
await JS.InvokeVoidAsync("registerFlatpickrYearChange", "input.flatpickr-input", _dotNetRef);           

The following client side script is registeret into the global window object to provide script event handlers that will be called when the end-user changes selected year or month, either via the UI controls or just entering the date.

datepicker-highlight.js

window.highlightFlatpickrDates = (selector, dates, highlightCssClass) => {
    //debugger
    const calendar = document.querySelector(selector); 
    if (!calendar) {
        return; //Wait for Flatpickr to render days
    }
    //debugger
    setTimeout(() => {
        //
        dates.forEach(date => {
            //debugger
            const dayElem = calendar.querySelector(`.flatpickr-day[aria-label="${date.date}"]`);
            if (dayElem) {
                dayElem.classList.add(highlightCssClass);
                dayElem.setAttribute('title', date.annotation);
            }
        });
    }, 50);
};

window.registerFlatpickrMonthChange = (selector, dotNetHelper) => {
    const fpInput = document.querySelector(selector);
    if (!fpInput || !fpInput._flatpickr) {
        setTimeout(() => window.registerFlatpickrMonthChange(selector, dotNetHelper), 50);
        return;
    }
    fpInput._flatpickr.config.onMonthChange.push(function () {
        dotNetHelper.invokeMethodAsync('OnMonthChanged');
    });
};

window.registerFlatpickrYearChange = (selector, dotNetHelper) => {
    const fpInput = document.querySelector(selector);
    if (!fpInput || !fpInput._flatpickr) {
        setTimeout(() => window.registerFlatpickrYearChange(selector, dotNetHelper), 50);
        return;
    }
    fpInput._flatpickr.config.onYearChange.push(function () {
        dotNetHelper.invokeMethodAsync('OnYearChanged');
    });
};

The following test page test out the component.

StyledDatePicker.razor

@page "/"
@using BlazoriseDatePickerWithHolidays.Components
@using BlazoriseDatePickerWithHolidays.Service
@using System.Globalization
@using static BlazoriseDatePickerWithHolidays.Service.HolidayService
@inject IHolidayService HolidayService

<h3>Custom Date Picker with Highlighted Days</h3>

<p>

    <b>The date picker used here is from Blazorise library and customized to allow setting days to highlight including tooltips annotating a description of the date being highlighted.</b>
    <br />
    Blazorise DatePicker component is described here:
    <br /><br />
    <a href="https://blazorise.com/docs/components/date-picker">https://blazorise.com/docs/components/date-picker</a>
    <br /><br />
    The highlighted dates selected for this demo are Christian Holidays and other public days off in Norway.
    In Norwegian, these days off are called 'Offentlige høytidsdager'.<br />
    These days are marked with a pink background, white foreground and rounded corners. <br />
    Tooltips are added showing the Holiday name <br/>

</p>

<div class="container-fluid">
    <div class="row">
        <div class="col-md-2">
            <CustomDatePicker
                @bind-SelectedDate="selectedDate" 
                Locale="en-US"
                FirstDayOfWeek="DayOfWeek.Monday"
                InputMode="DateInputMode.DateTime"
                DisplayFormat="HH:mm dd.MM.yyyy"
                InputFormat="HH:mm dd.MM.yyyy"
                TimeAs24hr="true"
                HighlightedDays="_holidays"
                @ref="@_datePicker" />
        </div>
    </div>
</div>

@{
    var chosenLocale = new CultureInfo(_datePicker?.Locale ?? "en-US");
}

<p class="mt-3">Selected date <strong>@selectedDate.ToString("HH:mm dd.MM.yyyy", chosenLocale)</strong></p>

@code {
    private DateTime selectedDate = new DateTime(2025, 5, 4);
    private static int minYear = DateTime.Today.AddYears(-20).Year;
    private List<AnnotatedDateTime>? _holidays;

    private CustomDatePicker? _datePicker;

    protected override void OnParametersSet()
    {  
        _holidays = Enumerable.Range(minYear, 40)
            .SelectMany(y => HolidayService.GetHolidays(y))
            .ToList();
    }

}

The dates to select uses an implementation of IHolidayService. This implemented like this, note that this finds 'Offentlige høytidsdager' and (Christian-belief) holidays in Norway.

HolidayService.cs

namespace BlazoriseDatePickerWithHolidays.Service;

public interface IHolidayService
{
    DateTime AddWorkingDaysToDate(DateTime date, int days);
    List<string> GetHolidayNames();
    IEnumerable<HolidayService.AnnotatedDateTime> GetHolidays(int year);
    bool IsHoliday(DateTime date);
    bool IsWorkingDay(DateTime date);
}

public partial class HolidayService : IHolidayService
{

    private static MemoryCache<int, HashSet<AnnotatedDateTime>> holidays = new();

    private static readonly List<string> holidayNames = new List<string> {
            "1. nyttårsdag",
            "Palmesøndag",
            "Skjærtorsdag",
            "Langfredag",
            "1. påskedag",
            "2. påskedag",
            "Offentlig høytidsdag",
            "Grunnlovsdag",
            "Kristi Himmelfartsdag",
            "1. pinsedag",
            "2. pinsedag",
            "1. juledag",
            "2. juledag"
    };

    /// <summary>
    /// Adds the given number of working days to the given date. A working day is
    /// specified as a regular Norwegian working day, excluding weekends and all
    /// national holidays.
    /// 
    /// Example 1:
    /// - Add 5 working days to Wednesday 21.03.2007 -> Yields Wednesday
    /// 28.03.2007. (skipping saturday and sunday)
    /// 
    /// Example 2:
    /// - Add 5 working days to Wednesday 04.04.2007 (day before
    /// easter-long-weekend) -> yields Monday 16.04.2007 (skipping 2 weekends and
    /// 3 weekday holidays).
    /// </summary>
    /// <param name="date">The original date</param>
    /// <param name="days">The number of working days to add</param>
    /// <returns>The new date</returns>
    public DateTime AddWorkingDaysToDate(DateTime date, int days)
    {
        var localDate = date;
        for (var i = 0; i < days; i++)
        {
            localDate = localDate.AddDays(1);
            while (!IsWorkingDay(localDate))
            {
                localDate = localDate.AddDays(1);
            }
        }
        return localDate;
    }

    /// <summary>
    /// Will check if the given date is a working day. That is check if the given
    /// date is a weekend day or a national holiday.
    /// </summary>
    /// <param name="date">The date to check</param>
    /// <returns>true if the given date is a working day, false otherwise</returns>
    public bool IsWorkingDay(DateTime date)
    {
        return date.DayOfWeek != DayOfWeek.Saturday && date.DayOfWeek != DayOfWeek.Sunday
               && !IsHoliday(date);
    }

    public List<string> GetHolidayNames()
    {
        return holidayNames;
    }

    /// <summary>
    /// Check if given Date object is a holiday.
    /// </summary>
    /// <param name="date">date to check if is a holiday</param>
    /// <returns>true if holiday, false otherwise</returns>
    public bool IsHoliday(DateTime date)
    {
        var year = date.Year;
        var holidaysForYear = GetHolidaySet(year);
        foreach (var holiday in holidaysForYear)
        {
            if (CheckDate(date, holiday.Value))
            {
                return true;
            }
        }
        return false;
    }

    /// <summary>
    /// Return a sorted array of holidays for a given year.
    /// </summary>
    /// <param name="year">The year to get holidays for</param>
    /// <returns>Holidays, sorted by date</returns>
    public IEnumerable<AnnotatedDateTime> GetHolidays(int year)
    {
        var days = GetHolidaySet(year);
        var listOfHolidays = new List<AnnotatedDateTime>(days);
        listOfHolidays.Sort((date1, date2) => date1.Value.CompareTo(date2.Value));
        return listOfHolidays;
    }

    /// <summary>
    /// Get a set of holidays for a given year
    /// </summary>
    /// <param name="year">The year to get holidays for</param>
    /// <returns>Holidays for year</returns>
    private IEnumerable<AnnotatedDateTime> GetHolidaySet(int year)
    {
        if (holidays == null)
        {
            holidays = new MemoryCache<int, HashSet<AnnotatedDateTime>>();
        }
        if (holidays.Get(year) == null)
        {
            var yearSet = new HashSet<AnnotatedDateTime>();

            // Add set holidays.
            yearSet.Add(new AnnotatedDateTime("1. nyttårsdag " + year, new DateTime(year, 1, 1)));
            yearSet.Add(new AnnotatedDateTime("Offentlig høytidsdag " + year, new DateTime(year, 5, 1)));
            yearSet.Add(new AnnotatedDateTime("Grunnlovsdag " + year, new DateTime(year, 5, 17)));
            yearSet.Add(new AnnotatedDateTime("1. juledag " + year, new DateTime(year, 12, 25)));
            yearSet.Add(new AnnotatedDateTime("2. juledag " + year, new DateTime(year, 12, 26)));

            // Add movable holidays - based on easter day.
            var easterDay = GetEasterDay(year);

            // Sunday before easter.
            yearSet.Add(new AnnotatedDateTime("Palmesøndag " + year, easterDay.AddDays(-7)));

            // Thurday before easter.
            yearSet.Add(new AnnotatedDateTime("Skjærtorsdag " + year, easterDay.AddDays(-3)));

            // Friday before easter.
            yearSet.Add(new AnnotatedDateTime("Langfredag " + year, easterDay.AddDays(-2)));

            // Easter day.
            yearSet.Add(new AnnotatedDateTime("1. påskedag " + year, easterDay));

            // Second easter day.
            yearSet.Add(new AnnotatedDateTime("2. påskedag " + year, easterDay.AddDays(1)));

            // "Kristi himmelfart" day.
            yearSet.Add(new AnnotatedDateTime("Kristi Himmelfartsdag " + year, easterDay.AddDays(39)));

            // "Pinse" day.
            yearSet.Add(new AnnotatedDateTime("1. pinsedag " + year, easterDay.AddDays(49)));

            // Second "Pinse" day.
            yearSet.Add(new AnnotatedDateTime("2. pinsedag " + year, easterDay.AddDays(50)));

            holidays.Add(year, yearSet);
        }
        return holidays.GetAsValue(year)!;
    }

    /// <summary>
    ///  Calculates easter day (sunday) by using Spencer Jones formula found here:
    ///  http://no.wikipedia.org/wiki/P%C3%A5skeformelen
    /// </summary>
    /// <param name="year">year</param>
    /// <returns>easterday for year</returns>
    private DateTime GetEasterDay(int year)
    {
        int a = year % 19;
        int b = year / 100;
        int c = year % 100;
        int d = b / 4;
        int e = b % 4;
        int f = (b + 8) / 25;
        int g = (b - f + 1) / 3;
        int h = (19 * a + b - d - g + 15) % 30;
        int i = c / 4;
        int k = c % 4;
        int l = (32 + 2 * e + 2 * i - h - k) % 7;
        int m = (a + 11 * h + 22 * l) / 451;
        int n = (h + l - 7 * m + 114) / 31; // This is the month number.
        int p = (h + l - 7 * m + 114) % 31; // This is the date minus one.

        return new DateTime(year, n, p + 1);
    }

    private bool CheckDate(DateTime date, DateTime other)
    {
        return date.Day == other.Day && date.Month == other.Month;
    }

}

Also, some CSS rules are added here for the custom control :

App.css

.flatpickr-day.pink-day {
    background: #ff69b4 !important; /* Hot pink */   
    color: white !important;
    border-radius: 50%;
}

.addon-margin {
    margin-left: 0.25rem !important; /* Adjust as needed */
}

Finally, a screenshot showing how the Custom date picker works. We have highlighted dates in May 2025 here, I chose to generate holidays for +- 20 years here. Obviously, an optimization would be the possibility to only pass in the chose year of the date picker and not a wide range of years. This is however looking to be fast anyways and I believe you can pass in a large number of dates to highlight here. Hopefully, this article has given you more inspiration how to add highlighting of dates into the Blazorise Datepicker component for Blazor !

Pluralizers in Entity Framework

In Entity Framework, you can implement a IPluralizationService to control how entities' names will be pluralized. In additional singularalized. The standard setup is an English pluralizer. In addition, a Spanish pluralizer is available. If you want to support another language for pluralization (and singularization), I have added a sample of this in the following Github repo of mine :

https://github.com/toreaurstadboss/BulkOperationsEntityFramework

Note that the Norwegian Pluralization service could also pluralize words in English and try to check if the word to pluralize is either English or Norwegian. It is about 500,000 English nouns and 100,000, so it might be hard to create a perfect pluralizer for both English or Norwegian. A list of about 40,000+ nouns are available here: https://gist.github.com/trag1c/f74b2ab3589bc4ce5706f934616f6195/ The Norwegian Pluralization service next could use that wordlist to check if the the word is English and use the standard built in English pluralizer service. I will give an updated version of the NorwegianPluralizationService at the end of the article.

NorwegianPluralizationService.cs

using System;
using System.Collections.Generic;
using System.Data.Entity.Infrastructure.Pluralization;
using System.Diagnostics;
using System.Linq;

namespace BulkOperationsEntityFramework.Lib.Services
{

    /// <summary>
    /// Sources for the pluralization rules for Norwegian language:
    /// https://toppnorsk.com/2018/11/18/flertall-hovedregler/
    /// </summary>
    public class NorwegianPluralizationService : IPluralizationService
    {

        public static List<string> PluralizedWords = new List<string>();

        public string Pluralize(string word)
        {
            if (PluralizedWords.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                return word; // Return the already pluralized word
            }

//#if DEBUG
//            Debugger.Break();
//            Debugger.Launch(); // Uncomment this line to break into the debugger when this method is called, for example when database migrations are made with EF Code First
//#endif

            word = NormalizeWord(word);

            string pluralizedWord;

            if (_specialCases.ContainsKey(word))
            {
                pluralizedWord = _specialCases[word];
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsChangingVowelToÆ.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                if (word.Equals("Håndkle", StringComparison.OrdinalIgnoreCase))
                {
                    pluralizedWord = "Håndklær";
                    PluralizedWords.Add(pluralizedWord);
                    return pluralizedWord;
                }
                pluralizedWord = word.Replace("å", "æ").Replace("e", "æ") + "r";
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsForUnits.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                pluralizedWord = word;
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsForRelatives.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                switch (word.ToLower())
                {
                    case "far": pluralizedWord = "Fedre"; break;
                    case "mor": pluralizedWord = "Mødre"; break;
                    case "datter": pluralizedWord = "Døtre"; break;
                    case "søster": pluralizedWord = "Søstre"; break;
                    case "fetter": pluralizedWord = "Fettere"; break;
                    case "onkel": pluralizedWord = "Onkler"; break;
                    case "svigerbror": pluralizedWord = "Svigerbrødre"; break;
                    case "svigerfar": pluralizedWord = "Svigerfedre"; break;
                    case "svigersøster": pluralizedWord = "Svigersøstre"; break;
                    case "svigermor": pluralizedWord = "Svigermødre"; break;
                    case "bror": pluralizedWord = "Brødre"; break;
                    default: pluralizedWord = word; break;
                }
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsNeutralGenderEndingWithEumOrIum.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                if (word.EndsWith("eum"))
                    pluralizedWord = word.Substring(0, word.Length - 3) + "eer";
                else if (word.EndsWith("ium"))
                    pluralizedWord = word.Substring(0, word.Length - 3) + "ier";
                else
                    pluralizedWord = word;
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsNoPluralizationForNeutralGenderOneSyllable.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                pluralizedWord = word;
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordChangingVowelsInPluralFemale.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                pluralizedWord = NormalizeWord(word.ToLower().Replace("å", "e").Replace("a", "e") + "er");
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_wordsChangingVowelsInPluralMale.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                string rewrittenWord = NormalizeWord(word.Replace("o", "ø"));
                if (rewrittenWord.Equals("føt", StringComparison.OrdinalIgnoreCase))
                    pluralizedWord = rewrittenWord + "ter";
                else if (rewrittenWord.EndsWith("e"))
                    pluralizedWord = rewrittenWord + "r";
                else if (!rewrittenWord.EndsWith("er"))
                    pluralizedWord = rewrittenWord + "er";
                else
                    pluralizedWord = rewrittenWord;
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_nonEndingWordsInPlural.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                pluralizedWord = word;
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            // General rules
            if (word.EndsWith("er"))
                pluralizedWord = word.Substring(0, word.Length - 2) + "ere";
            else if (word.EndsWith("el"))
                pluralizedWord = word.Substring(0, word.Length - 2) + "ler";
            else if (word.EndsWith("e"))
                pluralizedWord = word + "r";
            else if (word.EndsWith("en"))
                pluralizedWord = word + "er";
            else
                pluralizedWord = word + "er";

            PluralizedWords.Add(pluralizedWord);
            return pluralizedWord;
        }

        public string Singularize(string word)
        {
            word = NormalizeWord(word);

            // Reverse special cases
            var specialSingular = _specialCases.FirstOrDefault(kvp => kvp.Value.Equals(word, StringComparison.OrdinalIgnoreCase));
            if (!specialSingular.Equals(default(KeyValuePair<string, string>)))
                return specialSingular.Key;

            // Words that are the same in singular and plural
            if (_nonEndingWordsInPlural.Contains(word, StringComparer.OrdinalIgnoreCase) ||
                _wordsNoPluralizationForNeutralGenderOneSyllable.Contains(word, StringComparer.OrdinalIgnoreCase) ||
                _wordsForUnits.Contains(word, StringComparer.OrdinalIgnoreCase))
                return word;

            // Irregulars and vowel changes (expand as needed)
            if (word.Equals("Bøker", StringComparison.OrdinalIgnoreCase)) return "Bok";
            if (word.Equals("Føtter", StringComparison.OrdinalIgnoreCase)) return "Fot";
            if (word.Equals("Brødre", StringComparison.OrdinalIgnoreCase)) return "Bror";
            if (word.Equals("Menn", StringComparison.OrdinalIgnoreCase)) return "Mann";
            if (word.Equals("Kvinner", StringComparison.OrdinalIgnoreCase)) return "Kvinne";
            if (word.Equals("Gutter", StringComparison.OrdinalIgnoreCase)) return "Gutt";
            if (word.Equals("Netter", StringComparison.OrdinalIgnoreCase)) return "Natt";
            if (word.Equals("Tær", StringComparison.OrdinalIgnoreCase)) return "Tå";
            if (word.Equals("Tenner", StringComparison.OrdinalIgnoreCase)) return "Tann";
            if (word.Equals("Trær", StringComparison.OrdinalIgnoreCase)) return "Tre";
            if (word.Equals("Knær", StringComparison.OrdinalIgnoreCase)) return "Kne";
            if (word.Equals("Bønder", StringComparison.OrdinalIgnoreCase)) return "Bonde";
            if (word.Equals("Hender", StringComparison.OrdinalIgnoreCase)) return "Hand";
            if (word.Equals("Døtre", StringComparison.OrdinalIgnoreCase)) return "Datter";
            if (word.Equals("Fedre", StringComparison.OrdinalIgnoreCase)) return "Far";
            if (word.Equals("Mødre", StringComparison.OrdinalIgnoreCase)) return "Mor";
            if (word.Equals("Søstre", StringComparison.OrdinalIgnoreCase)) return "Søster";
            if (word.Equals("Øyne", StringComparison.OrdinalIgnoreCase)) return "Øye";

            // "ler" ending (from "el")
            if (word.EndsWith("ler"))
            {
                return word.Substring(0, word.Length - 2);
            }
            if (word.EndsWith("ter"))
            {
                return word.Substring(0, word.Length - 1);
            }

            // "ere" ending (from "er" ending in singular, e.g. "Lærere" -> "Lærer")
            if (word.EndsWith("ere"))
                return word.Substring(0, word.Length - 1);

            // "er" ending (general case, e.g. "Biler" -> "Bil", "Stoler" -> "Stol", "Jenter" -> "Jente")
            if (word.EndsWith("er"))
                return word.Substring(0, word.Length - 2);

            // "r" ending (from "e" ending in singular, e.g. "Jenter" -> "Jente" already handled above)
            if (word.EndsWith("r"))
            {
                var possibleSingular = word.Substring(0, word.Length - 1);
                return possibleSingular;
            }

            // Default: return as is
            return word;
        }

        /// <summary>
        /// Make the world normalized, i.e. first letter upper case and rest lower case letters, the word is trimmed.
        /// Not considering using invariant culture here, as this is a Norwegian pluralization service.
        /// </summary>
        /// <remarks>In case an empty word (null or empty) is passed in, just return the word.
        /// Edge case: In case just One non-empty letter was passed in, make the word also uppercase.</remarks>
        private string NormalizeWord(string word)
        {
            word = word?.Trim();
            if (string.IsNullOrEmpty(word) || word.Trim().Length <= 1) {
                return word?.ToUpper();
            }
            return word.Substring(0, 1).ToUpper() + word.Trim().ToLower().Substring(1);
        }

        private string[] _nonEndingWordsInPlural = new string[] {
            "mus", "sko", "ski", "feil", "ting" }; // Add more non-ending words in plural as needed

        private string[] _wordsChangingVowelsInPluralMale = new string[]
        {
            "bonde", "fot", "bok", "bot", "rot"
        };

        private Dictionary<string, string> _specialCases = new Dictionary<string, string>
        {
            { "Mann", "Menn" } , // 'mann' => 'menn'
            { "Barn", "Barn" }, // 'barn' => 'barn' (no pluralization)
            { "Øye", "Øyne" }, // 'øye' => 'øyne' (plural form of 'eye') //consider adding more special cases here in case all the other pluralization rules do not cover the given word
        };

        private string[] _wordsChangingVowelToÆ = new string[]
        {
            "Håndkle", "Kne", "Tre", "Tå"
        };

        private string[] _wordsForUnits = new string[]
        {
            "meter", "centimeter", "millimeter", "kilometer", "gram", "kilogram", "tonn", "liter", "desiliter", "centiliter", "dollar", "lire",
            "pesetas", "euro", "yen", "franc", "pund", "rupee", "ringgit", "peso", "real", "won", "yuan"
        };

        private string[] _wordChangingVowelsInPluralFemale = new string[]
        {
            "and", "hand", "hånd", "natt", "stang", "strand", "tang", "tann"
        };

        private string[] _wordsForRelatives = new string[]
        {
            "far", "mor", "datter", "fetter", "onkel", "bror", "svigerbror", "svigerfar", "svigermor", "svigersøster", "søster"
        };

        private string[] _wordsNoPluralizationForNeutralGenderOneSyllable = new string[]
        {
            "hus", "fjell", "blad"
        };

        private string[] _wordsNeutralGenderEndingWithEumOrIum = new string[]
        {
            "museum", "Jubileum", "kjemikalium"
        };

    }
}

The following DbConfiguration set up for the DbContext sets up the pluralization service to use for Entity Framework.

ApplicationDbConfiguration.cs

using BulkOperationsEntityFramework.Lib.Services;
using System;
using System.Data.Entity;
using System.Data.Entity.SqlServer;

namespace BulkOperationsEntityFramework
{
    public class ApplicationDbConfiguration : DbConfiguration
    {

        public ApplicationDbConfiguration()
        {
        
            SetPluralizationService(new NorwegianPluralizationService());  //Set up the NorwegianPluralizationService as the Pluralizer         
            
            //more code etc..
        }

    }

}

I have also created a Schema attribute to control schema names of tables convention previously in the solution, so the Norwegian pluralizer is also being used there.

SchemaConvention.cs

using BulkOperationsEntityFramework.Attributes;
using BulkOperationsEntityFramework.Lib.Services;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Reflection;

namespace BulkOperationsEntityFramework.Conventions
{
    public class SchemaConvention : Convention
    {
        public SchemaConvention()
        {
            var pluralizer = new NorwegianPluralizationService();

            Types().Configure(c =>
            {
                var schemaAttr = c.ClrType.GetCustomAttribute<SchemaAttribute>(false);
                var tableName = pluralizer.Pluralize(c.ClrType.Name);

                if (schemaAttr != null && !string.IsNullOrEmpty(schemaAttr.SchemaName))
                {
                    c.ToTable(tableName, schemaAttr.SchemaName ?? "dbo");
                }
                else
                {
                    c.ToTable(tableName);
                }
            });
        }
    }
}

The DbContext will use the IPluralizationService. Consider first this example DbContext :

ApplicationDbContext

using BulkOperationsEntityFramework.Conventions;
using BulkOperationsEntityFramework.Models;
using BulkOperationsEntityFramework.Test;
using System;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Infrastructure.Interception;
using System.Linq;

namespace BulkOperationsEntityFramework
{

    [DbConfigurationType(typeof(ApplicationDbConfiguration))]
    public class ApplicationDbContext : DbContext
    {       

        public ApplicationDbContext(DbConnection connection) : base(connection, false)
        {
        }

        public ApplicationDbContext() : base("name=App")
        {
        }

        public virtual DbSet Bruker { get; set; }

        public DbSet ArkivertBruker { get; set; }

        public DbSet ArkivertGjest { get; set; }

        public DbSet Sesjon { get; set; }

        public DbSet Jubileum { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {            
            modelBuilder.Conventions.Add(new SchemaConvention());
            //more code etc
          
        }

    }

}

The following test cases checks how good the pluralizer works.

ApplicationDbContextTests.cs

using Bogus;
using BulkOperationsEntityFramework.Lib.Services;
using BulkOperationsEntityFramework.Models;
using FluentAssertions;
using Moq;
using Newtonsoft.Json;
using NUnit.Framework;
using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Infrastructure.Interception;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;

namespace BulkOperationsEntityFramework.Test
{

    [TestFixture]
    public class ApplicationDbContextTests
    {

       
        [Test]
        [TestCaseSource(nameof(NorwegianPluralizationCases))]
        public void CanUsePluralizationService(string word, string expected)
        {
            var norwegianPluralizationService = new NorwegianPluralizationService();
            string pluralizedWord = norwegianPluralizationService.Pluralize(word);
            pluralizedWord.Should().Be(expected, "Norwegian Pluralization service should return the correct plural form of the word.");
        }

        [Test, TestCaseSource(nameof(NorwegianSingularizationCases))]
        public void NorwegianPluralizationService_CanSingularize(string plural, string expectedSingular)
        {
            var norwegianPluralizationService = new NorwegianPluralizationService();

            var actual = norwegianPluralizationService.Singularize(plural);
            Assert.That(actual, Is.EqualTo(expectedSingular), $"Expected singular of '{plural}' to be '{expectedSingular}', but got '{actual}'.");
        }

        public static IEnumerable<TestCaseData> NorwegianPluralizationCases
        {
            get
            {
                yield return new TestCaseData("Bil", "Biler");
                yield return new TestCaseData("Bok", "Bøker");
                yield return new TestCaseData("Hund", "Hunder");
                yield return new TestCaseData("Stol", "Stoler");
                yield return new TestCaseData("Jente", "Jenter");
                yield return new TestCaseData("Gutt", "Gutter");
                yield return new TestCaseData("Lærer", "Lærere");
                yield return new TestCaseData("Barn", "Barn");
                yield return new TestCaseData("Fjell", "Fjell");
                yield return new TestCaseData("Sko", "Sko");
                yield return new TestCaseData("Ting", "Ting");
                yield return new TestCaseData("Mann", "Menn");
                yield return new TestCaseData("Kvinne", "Kvinner");
                yield return new TestCaseData("Bror", "Brødre");
                yield return new TestCaseData("Far", "Fedre");
                yield return new TestCaseData("Mor", "Mødre");
                yield return new TestCaseData("Datter", "Døtre");
                yield return new TestCaseData("Søster", "Søstre");
                yield return new TestCaseData("Øye", "Øyne");
                yield return new TestCaseData("Hand", "Hender");
                yield return new TestCaseData("Fot", "Føtter");
                yield return new TestCaseData("Tå", "Tær");
                yield return new TestCaseData("Tann", "Tenner");
                yield return new TestCaseData("Natt", "Netter");
                yield return new TestCaseData("Tre", "Trær");
                yield return new TestCaseData("Kne", "Knær");
                yield return new TestCaseData("Bonde", "Bønder");

                // _nonEndingWordsInPlural
                yield return new TestCaseData("Mus", "Mus");
                yield return new TestCaseData("Ski", "Ski");
                yield return new TestCaseData("Feil", "Feil");

                // _wordsChangingVowelsInPluralMale
                yield return new TestCaseData("Bot", "Bøter");
                yield return new TestCaseData("Rot", "Røter");

                // _wordsChangingVowelToÆ
                yield return new TestCaseData("Håndkle", "Håndklær");
                yield return new TestCaseData("Kne", "Knær");

                // _wordsForUnits (should not pluralize)
                yield return new TestCaseData("Meter", "Meter");
                yield return new TestCaseData("Gram", "Gram");
                yield return new TestCaseData("Dollar", "Dollar");

                // _wordChangingVowelsInPluralFemale
                yield return new TestCaseData("And", "Ender");
                yield return new TestCaseData("Hånd", "Hender");
                yield return new TestCaseData("Stang", "Stenger");
                yield return new TestCaseData("Strand", "Strender");
                yield return new TestCaseData("Tang", "Tenger");
                yield return new TestCaseData("Tann", "Tenner");

                // _wordsForRelatives (some already covered, but add missing)
                yield return new TestCaseData("Fetter", "Fettere");
                yield return new TestCaseData("Onkel", "Onkler");
                yield return new TestCaseData("Svigerbror", "Svigerbrødre");
                yield return new TestCaseData("Svigerfar", "Svigerfedre");
                yield return new TestCaseData("Svigermor", "Svigermødre");
                yield return new TestCaseData("Svigersøster", "Svigersøstre");

                // _wordsNoPluralizationForNeutralGenderOneSyllable
                yield return new TestCaseData("Hus", "Hus");
                yield return new TestCaseData("Blad", "Blad");

                // _wordsNeutralGenderEndingWithEumOrIum
                yield return new TestCaseData("Museum", "Museer");
                yield return new TestCaseData("Jubileum", "Jubileer");
                yield return new TestCaseData("Kjemikalium", "Kjemikalier");
            }
        }

        public static IEnumerable<TestCaseData> NorwegianSingularizationCases
        {
            get
            {
                yield return new TestCaseData("Biler", "Bil");
                yield return new TestCaseData("Bøker", "Bok");
                yield return new TestCaseData("Hunder", "Hund");
                yield return new TestCaseData("Stoler", "Stol");
                yield return new TestCaseData("Jenter", "Jente");
                yield return new TestCaseData("Gutter", "Gutt");
                yield return new TestCaseData("Lærere", "Lærer");
                yield return new TestCaseData("Barn", "Barn");
                yield return new TestCaseData("Fjell", "Fjell");
                yield return new TestCaseData("Sko", "Sko");
                yield return new TestCaseData("Ting", "Ting");
                yield return new TestCaseData("Menn", "Mann");
                yield return new TestCaseData("Kvinner", "Kvinne");
                yield return new TestCaseData("Brødre", "Bror");
                yield return new TestCaseData("Fedre", "Far");
                yield return new TestCaseData("Mødre", "Mor");
                yield return new TestCaseData("Døtre", "Datter");
                yield return new TestCaseData("Søstre", "Søster");
                yield return new TestCaseData("Øyne", "Øye");
                yield return new TestCaseData("Hender", "Hand");
                yield return new TestCaseData("Føtter", "Fot");
                yield return new TestCaseData("Tær", "Tå");
                yield return new TestCaseData("Tenner", "Tann");
                yield return new TestCaseData("Netter", "Natt");
                yield return new TestCaseData("Trær", "Tre");
                yield return new TestCaseData("Knær", "Kne");
                yield return new TestCaseData("Bønder", "Bonde");
            }
        }

    }
}

The pluralization is used when creating migrations and map entites to table names. The following migration shows how the Norwegian pluralization has pluralized the table names.

202506292302222_Init.cs

namespace BulkOperationsEntityFramework.Migrations
{
    using System.Data.Entity.Migrations;

    public partial class Init : DbMigration
    {
        public override void Up()
        {
            CreateTable(
                "Archive.Arkivertbrukere",
                c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Email = c.String(maxLength: 255),
                    FirstName = c.String(maxLength: 255),
                    LastName = c.String(maxLength: 255),
                    PhoneNumber = c.String(maxLength: 255),
                })
                .PrimaryKey(t => t.Id);

            CreateTable(
                "Arkiv.Gjester",
                c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Email = c.String(maxLength: 255),
                    FirstName = c.String(maxLength: 255),
                    LastName = c.String(maxLength: 255),
                })
                .PrimaryKey(t => t.Id);

            CreateTable(
                "dbo.Brukere",
                c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Email = c.String(maxLength: 255),
                    FirstName = c.String(maxLength: 255),
                    LastName = c.String(maxLength: 255),
                    PhoneNumber = c.String(maxLength: 255),
                })
                .PrimaryKey(t => t.Id);

            CreateTable(
                "dbo.Jubileer",
                c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Date = c.DateTime(),
                    Description = c.String(maxLength: 255),
                })
                .PrimaryKey(t => t.Id);

            CreateTable(
                "dbo.Sesjoner",
                c => new
                {
                    Key = c.Guid(nullable: false),
                    CreatedAt = c.DateTime(nullable: false),
                    ExpiresAt = c.DateTime(),
                    IpAddress = c.String(maxLength: 255),
                    UserAgent = c.String(maxLength: 255),
                })
                .PrimaryKey(t => t.Key);

        }

        public override void Down()
        {
            DropTable("dbo.Sesjoner");
            DropTable("dbo.Jubileer");
            DropTable("dbo.Brukere");
            DropTable("Arkiv.Gjester");
            DropTable("Archive.Arkivertbrukere");
        }
    }
}

The table names above are pluralized into their Norwegian pluralization. In Norwegian we call these words "ubestemt flertall", indefinite plural. It is possible to add detection if the passed in noun is an English noun. But beware that there are several Norwegian nouns overlapping these English nouns. So in fairness, a Norwegian wordlist should also be checked. However, the following update only shows how an English dictionary can be checked. The English noun list is put into a static variable into memory for quick access. The world list I have tested with got about 40,0000+ noun as mentioned previously in this article.

NorwegianPluraizationService.cs

(updated with a check against a English noun list and using the default EnglishPluralizationService that Entity Framework contains to add support for English noun pluralization (and singularization)

using System;
using System.Collections.Generic;
using System.Data.Entity.Infrastructure.Pluralization;
using System.IO;
using System.Linq;
using System.Reflection;

namespace BulkOperationsEntityFramework.Lib.Services
{

    /// <summary>
    /// Sources for the pluralization rules for Norwegian language:
    /// https://toppnorsk.com/2018/11/18/flertall-hovedregler/
    /// </summary>
    public class NorwegianPluralizationService : IPluralizationService
    {
        private EnglishPluralizationService _englishPluralizationService = new EnglishPluralizationService();
        
        public static List<string> PluralizedWords = new List<string>();

        private static List<string> EnglishNounsWordList = null;

        public string Pluralize(string word)
        {
            if (PluralizedWords.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                return word; // Return the already pluralized word
            }

            //#if DEBUG
            //            Debugger.Break();
            //            Debugger.Launch(); // Uncomment this line to break into the debugger when this method is called, for example when database migrations are made with EF Code First
            //#endif

            word = NormalizeWord(word);

            if (EnglishNounsWordList == null)
            {
                EnglishNounsWordList = new List<string>();
                var assembly = typeof(NorwegianPluralizationService).Assembly;
                // Adjust the resource name to match your project's default namespace and folder structure
                var resourceName = "BulkOperationsEntityFramework.Lib.Services.EnglishNouns.txt";
                using (var stream = assembly.GetManifestResourceStream(resourceName))
                using (var reader = new StreamReader(stream))
                {
                    EnglishNounsWordList.AddRange(reader.ReadToEnd().Split('\n').Select(l => l.Trim()));
                }
            }

            string pluralizedWord;

            if (EnglishNounsWordList.Contains(word, StringComparer.OrdinalIgnoreCase))
            {
                pluralizedWord = _englishPluralizationService.Pluralize(word);
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }

            if (_specialCases.ContainsKey(word))
            {
                pluralizedWord = _specialCases[word];
                PluralizedWords.Add(pluralizedWord);
                return pluralizedWord;
            }
            
            //more code

To sum up, we can customize Entity Framework pluralization to support other languages. But please note that there is a lot of work to make a good pluralization service. Also, you probably want to support English nouns too. The last version above did not use a Norwegian wordlist. A better pluralization service could directly try to lookup pluralized and singularized nouns of both languages instead of all the general and specific rules presented in these code samples. The English pluralization service do not do this, instead it relies on rule sets, such as the first version of
the Norwegian pluralizer shown earlier in this article is using.