Monday, 28 December 2020

Live reloads for Blazor - and a simple clock component

This article will test out Blazor. I had some difficulties with getting live reload to work. I got it working in Visual Studio 2019 for the Blazor Asp.Net Core project template. We will also create a very simple component (a clock) that calls Javascript function from C#. You can clone the simple app of mine from Github like this:
 git clone
First off, we add the following into _host.cshtml :
<script src="js/script.js"></script> <script src="_framework/blazor.server.js"></script> <script> Blazor.defaultReconnectionHandler._reconnectCallback = function (d) { document.location.reload(); } </script>
The Blazor.defaultReconnectionHandler._reconnectCallback is set to reload the document location This makes the page reload when you edit the razor files of the Blazor app. You will see this as a temporarily recompile step - give it some 5 seconds in a simple app.
Let's for fun add a clock component also. Add to the Shared folder the file Clock.razor.
@inject IJSRuntime JsRunTime @implements IDisposable

The time is now:

@code { ElementReference timeDiv; protected override async Task OnAfterRenderAsync(bool firstRender) { if (firstRender) { await JsRunTime.InvokeVoidAsync("startTime", timeDiv); } } public void Dispose() { JsRunTime.InvokeVoidAsync("stopTime"); } }
And we have also the script.js file in wwwroot to add some Javascript (Blazor razor files dont like Js in the component itself, just make sure to add the Js somewhere in wwwroot instead which loads up the necessary Js). As you can see we inject with the @inject in the razor Blazor file (rhymes a bit) the IJsRunTime. This allows us to call client-side code from the C# code. We start off the clock with a setTimeout and stop the clock with a clearTimeout.
var clock; function startTime(element) { let timeString = new Date().toLocaleTimeString('nb-No', { hour: 'numeric', hour12: false, minute: 'numeric', second: 'numeric' }); element.innerHTML = timeString; clock = setTimeout(startTime.bind(null, element), 1000); } function stopTime() { clearTimeout(clock); }

Sunday, 27 December 2020

GraphQL in Asp.Net Core - Creating a flexible API

More and more .NET Developers have heard about GraphQL. This started as an in-house project in Facebook 2012 to provide a flexible way of sending customized data to mobile clients. Giving the clients the possible to query after tailored data meant sending less data over the wire to the mobiles with less bandwidth. As cell phones moves over to 5G networks, the issue means less and less (in urban areas with good base station coverage), however we should of course seek to always optimize our data transfer as pure bandwidth usage is always a valued thing to optimize. And added dimension is the less cost of creating APIs as we can tailor our data needs. Instead of creating methods for either returning lookup ids and then querying after entire data objects, we can project only the data we need to retrieve to present data on the mobile clients in a meaningful way. Whatever makes your boat rock for showing interest in GraphQL, this article will discuss how you can get started with GraphQL in Asp.Net Core. I have prepared a demo here:
The demo repository shows a list of the tallest mountains in the municipialites in Norway. Norway is a land of mountains and it is always to know which mountain is the very tallest in the municipiality you are visiting! (I enjoy mountain climbing and hiking now and then in my spare time). The demo page shows a text area where you can customize the data to load here. Of course we can only load the data provided for us. We can also use the Ui playground for GraphQL added for us here too:
First off, we need to grab some Nuget packages for GraphQL. We will be using Asp.Net Core 3.1. in this article.
        <PackageReference Include="GraphQL" Version="2.4.0" />
	<PackageReference Include="GraphQL.Server.Transports.AspNetCore" Version="3.4.0" />
	<PackageReference Include="GraphQL.Server.Transports.WebSockets" Version="3.4.0" />
	<PackageReference Include="GraphQL.Server.Ui.Playground" Version="3.5.0-alpha0046" />  
Then we need to specify in our Startup class the needed setup.
using AspNetCore_GraphQLDemo.GraphQL; using AspNetCore_GraphQLDemo.GraphQL.Messaging; using Data; using Data.Repositories; using GraphQL; using GraphQL.Server; using GraphQL.Server.Ui.Playground; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Diagnostics; using Microsoft.AspNetCore.Hosting; using Microsoft.AspNetCore.Http; using Microsoft.AspNetCore.WebSockets; using Microsoft.EntityFrameworkCore; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.DependencyInjection; using Microsoft.Extensions.Hosting; using Newtonsoft.Json; namespace AspNetCore_GraphQLDemo { public class Startup { private readonly IWebHostEnvironment _env; public Startup(IConfiguration configuration, IWebHostEnvironment env) { _env = env; Configuration = configuration; } public IConfiguration Configuration { get; } // This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) { // If using IIS: services.Configure<IISServerOptions>(options => { options.AllowSynchronousIO = true; }); services.AddControllersWithViews(); services.AddHttpContextAccessor(); services.AddRazorPages().AddRazorRuntimeCompilation(); services.AddDbContext<MountainDbContext>(options => { options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")); }); services.AddScoped<IMountainRepository, MountainRepository>(); services.AddScoped<IDependencyResolver>(s => new FuncDependencyResolver(s.GetRequiredService)); services.AddScoped<MountainSchema>(); services.AddSingleton<MountainMessageService>(); services.AddSingleton<MountainDetailsDisplayedMessageService>(); services.AddGraphQL(x => { x.EnableMetrics = true; x.ExposeExceptions = _env.IsDevelopment(); x.SetFieldMiddleware = true; }).AddGraphTypes(ServiceLifetime.Scoped) .AddUserContextBuilder(httpContext => httpContext.User) .AddDataLoader() .AddWebSockets(); services.AddCors(options => { options.AddPolicy(name: "MyAllowSpecificOrigins", builder => { builder.AllowAnyOrigin().AllowAnyMethod(); }); }); } //static IEnumerable<Type> GetGraphQlTypes() //{ // return typeof(Startup).Assembly // .GetTypes() // .Where(x => !x.IsAbstract && // (typeof(IObjectGraphType).IsAssignableFrom(x) || // typeof(IInputObjectGraphType).IsAssignableFrom(x))); //} // This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); app.UseBrowserLink(); } app.UseExceptionHandler(errorApp => { errorApp.Run(async context => { context.Response.Redirect("/Error"); context.Response.StatusCode = 500; var exceptionHandlerPathFeature = context.Features.Get<IExceptionHandlerPathFeature>(); var exception = exceptionHandlerPathFeature.Error; var result = JsonConvert.SerializeObject(new { error = exception.Message }); context.Response.ContentType = "application/json"; await context.Response.WriteAsync(result); }); }); app.UseStaticFiles(); app.UseRouting(); app.UseCors("MyAllowSpecificOrigins"); app.UseWebSockets(); app.UseGraphQLWebSockets<MountainSchema>("/graphql"); //app.UseAuthorization(); app.UseEndpoints(endpoints => { endpoints.MapDefaultControllerRoute(); }); app.UseGraphQL<MountainSchema>(); if (env.IsDevelopment()) { app.UseGraphQLPlayground(new GraphQLPlaygroundOptions { }); } } } }
In ConfigureServices method above we register the schema for our GraphQL method.
We also add GraphQL itself and setup also web sockets (which are needed for GraphQL).
       services.AddGraphQL(x =>
                    x.EnableMetrics = true; x.ExposeExceptions = _env.IsDevelopment(); x.SetFieldMiddleware = true; }).AddGraphTypes(ServiceLifetime.Scoped)
            .AddUserContextBuilder(httpContext => httpContext.User)
Just as a side note, you want to add Cors also:
     services.AddCors(options =>
                options.AddPolicy(name: "MyAllowSpecificOrigins",
                    builder =>
Inside Configure method we add also the following to enable GraphQL:




            app.UseEndpoints(endpoints =>

            if (env.IsDevelopment())
                app.UseGraphQLPlayground(new GraphQLPlaygroundOptions
Our Mountainschema looks like this:
using AspNetCore_GraphQLDemo.GraphQL.Types; using AspNetCore_GraphQLDemo.GraphQL.Types.Directives; using GraphQL; using GraphQL.Instrumentation; using GraphQL.Types; namespace AspNetCore_GraphQLDemo.GraphQL { public class MountainSchema : Schema { public MountainSchema(IDependencyResolver resolver) : base(resolver) { Query = resolver.Resolve<MountainQuery>(); Mutation = resolver.Resolve<MountainMutation>(); Subscription = resolver.Resolve<MountainSubscription>(); RegisterDirective(new LowercaseDirective()); RegisterDirective(new OrderbyDirective()); var builder = new FieldMiddlewareBuilder(); builder.Use<LowercaseFieldsMiddleware>(); builder.ApplyTo(this); builder.Use(next => { return context => { return next(context).ContinueWith(x => { var c = context; var result = x.Result; result = OrderbyQuery.OrderIfNecessary(context, result); return result; }); }; }); builder.ApplyTo(this); //builder.Use<CustomGraphQlExecutor<MountainSchema>>(); //builder.ApplyTo(this); } } }
We pass in a IDependencyResolver (dependency!) into the constructor and resolve the classes we desire (we inherit from Schema class). We wire up our schema here to the Query, Mutation and Subscription we desire and register directives. Here is how the Query property is set:
using AspNetCore_GraphQLDemo.GraphQL.Types; using Data; using Data.Repositories; using GraphQL.Types; namespace AspNetCore_GraphQLDemo.GraphQL { public class MountainQuery : ObjectGraphType { public MountainQuery(IMountainRepository mountainRepository) { Field<ListGraphType<MountainType>>("mountains", resolve: context => mountainRepository.GetAll() ); FieldAsync<MountainType>("mountain", arguments: new QueryArguments(new QueryArgument<NonNullGraphType<MountainIdInputType>> {Name = "id"}), resolve: async context => { var mountain = context.GetArgument<MountainInfo>("id"); var mountainFromDb = await mountainRepository.GetById(mountain.Id); return mountainFromDb; }); //FieldAsync<MountainType>("selectmountain", // arguments: new QueryArguments(new QueryArgument(typeof(int)) { Name = "id" }), // resolve: async context => // { // var mountain = context.GetArgument<MountainInfo>("id"); // var mountainFromDb = await mountainRepository.GetById(mountain.Id); // return mountainFromDb; // }); //sadly, we need to inherit from IGraphType and cannot just have simple scalar arguments in GraphQL.Net.. } } }
As you can see, we can define multiple queries. We inherit from ObjectGraphType and pass in a IMountainRepository. This is an interface for your repository, which fetches data via Entity Framework Core and you can then load data into GraphQL from the local database (The DEMO uses Sql Server (SQLEXPRESS)) via EF Core in a simple manner by only providing the repo via dependency injection. We define via the methods Field and FieldAsync our methods (note the use of string constants as a string value we can use in GraphQL queries of ours that resides in the Schema) and the resolve lambda tells how data is to be fetched. We can specify arguments also. The "mountain" FieldAsync method also accepts arguments via the
arguments lambda and this allows us parameterized access to our data. Over to the Subscription property. It looks like this:
using AspNetCore_GraphQLDemo.GraphQL.Messaging;
using AspNetCore_GraphQLDemo.GraphQL.Types;
using GraphQL.Resolvers;
using GraphQL.Types;

namespace AspNetCore_GraphQLDemo.GraphQL
    public class MountainSubscription : ObjectGraphType
        public MountainSubscription(MountainDetailsDisplayedMessageService mountainDetailsDisplayedMessageService)
            Name = "Subscription";
            AddField(new EventStreamFieldType
                Name = "detailsDisplayed",
                Type = typeof(MountainDetailsMessageType),
                Resolver = new FuncFieldResolver<MountainDetailsMessage>(c => c.Source as MountainDetailsMessage),
                Subscriber = new EventStreamResolver<MountainDetailsMessage>(c => mountainDetailsDisplayedMessageService.GetMessages())
Here we inherit from ObjectGraphType (as we did for Query) and we use the MountainDetailsDisplayedMessageService. This was added as a (concrete class) singleton in the Startup.cs file. The message service uses RxJs serverside to handle the Pub-sub pattern of the subscriber. We are using System.Reactive.Subjects here.
using System; using System.Reactive.Linq; using System.Reactive.Subjects; namespace AspNetCore_GraphQLDemo.GraphQL.Messaging { public class MountainDetailsDisplayedMessageService { private readonly ISubject<MountainDetailsMessage> _messageStream = new ReplaySubject<MountainDetailsMessage>(1); public MountainDetailsMessage AddMountainDetailsMessage(int id) { var message = new MountainDetailsMessage { Id = id }; _messageStream.OnNext(message); return message; } public IObservable<MountainDetailsMessage> GetMessages() { return _messageStream.AsObservable(); } } }
The mutation looks like this:
using AspNetCore_GraphQLDemo.GraphQL.Messaging; using AspNetCore_GraphQLDemo.GraphQL.Types; using Data; using Data.Repositories; using GraphQL.Types; namespace AspNetCore_GraphQLDemo.GraphQL { public class MountainMutation : ObjectGraphType { public MountainMutation(IMountainRepository mountainRepository, MountainMessageService mountainMessageService) { FieldAsync<MountainType>("createMountain", arguments: new QueryArguments( new QueryArgument<NonNullGraphType<MountainInputType>> {Name = "mountain"}), resolve: async context => { var mountain = context.GetArgument<MountainInfo>("mountain"); await mountainRepository.AddMountain(mountain); mountainMessageService.AddMountainAddedMessage(mountain); return mountain; }); FieldAsync<MountainType>("removeMountain", arguments: new QueryArguments( new QueryArgument<NonNullGraphType<MountainIdInputType>> { Name = "id" }), resolve: async context => { var mountain = context.GetArgument<MountainInfo>("id"); await mountainRepository.RemoveMountain(mountain.Id); return mountain; }); } } }
We can create a mountain like this in GraphQL Query:
 mutation {
  createMountain(mountain: {
   county: "Svalbard"
  muncipiality: "Svalbard"
  officialName: "Newtontoppen"
  referencePoint: "Isbjønn på toppen"
  comments: "Husk rask snøskuter",
  metresAboveSeaLevel: "1713",
  primaryFactor: "1713"
  }) {    
And we can remove a mountain (don't we all?) like this:

# Write your query or mutation here
mutation {
  removeMountain(id: {
    id: 370
  }) { id }
If you clone the repo you will find more source code concerning directives such as lowercase and sorting. As you saw in MountainSchema I use the FieldMiddlewareBuilder to do the sorting as this needs to tap into the pipeline more of GraphQL.Net. We also need some more code - for the client side of course. The client side code relies on Apollo Client lib like this:
<script src=""></script>
The libman.json file (the similar file to package.json when it comes to specifying client-side libraries in .net core mvc solutions) of the demo solution looks like this I have used looks like this:
{ "version": "1.0", "defaultProvider": "cdnjs", "libraries": [ { "library": "twitter-bootstrap@4.2.1", "destination": "wwwroot/lib/bootstrap", "files": [ "js/bootstrap.bundle.js", "css/bootstrap.min.css" ] }, { "library": "jquery@3.3.1", "destination": "wwwroot/lib/jquery", "files": [ "jquery.min.js" ] }, { "provider": "unpkg", "library": "font-awesome@4.7.0", "destination": "wwwroot/lib/font-awesome/" }, { "provider": "unpkg", "library": "toastr@2.1.4", "destination": "wwwroot/lib/toastr/" } ] }
We then need some client side code to load data from GraphQL server of ours.

    function LoadGraphQLDataIntoUi(result) {

        var tableBody = $("#mountainsTableBody");

        var tableHeaderRow = $("#mountainsTableHeaderRow");

        var rowIndex = 0; => {

            if (rowIndex == 0) {
                Object.keys(mountain).forEach(key => {
                    if (key === '__typename') {


            Object.keys(mountain).forEach(key => {
                if (key === '__typename') {
                if (key === 'id') {
                    tableBody.append(`<td><a href='/home/mountaindetails/?id=${mountain[key]}'><i class='fa fa-arrow-right'></i></a> ${mountain[key]}</td>`);





        toastr.success('Loaded GraphQL data from server into the UI successfully.');


    $("#btnConnect").click(function () {


    $("#btnLoadData").click(function () {
        var gqlQueryContents = $("#GraphQLQuery").val();
        LoadGraphQLData(gqlQueryContents, LoadGraphQLDataIntoUi);'Retrieving data from API using GraphQL.');

    $(document).ready(function () {


        var initialQuery = `
                    mountains {
                        fylke: county
                        kommune: muncipiality
                        hoydeOverHavet: calculatedMetresAboveSeaLevel
                        offisieltNavn: officialName
                        primaerfaktor: calculatedPrimaryFactor
                        referansePunkt: referencePoint



And then a method using Apollo client lib to load the data:
 * Loads GraphQL data specified by query expression and passes the 'result' array to the callBackFunction
 * callBackFunction should be Js method (function) that accept one parameter, preferably called result, which is an object
 * that contains a object.
function LoadGraphQLData(gqlQuery, callBackFunction) {

    var apolloClient = new Apollo.lib.ApolloClient({
        networkInterface: Apollo.lib.createNetworkInterface({
            uri: 'http://localhost:2542/graphql',
            transportBatching: true,
        }), connectToDevTools: true
    var query = Apollo.gql(gqlQuery);

        query: query,
        variables: {}
    }).then(result => {
    }).catch(error => {
        toastr.error(error, 'GraphQL loading failed');

Friday, 25 December 2020

Generic memory cache and middleware in Asp.Net Core

In this article I will present code for creating added functionality to IMemoryCache in Asp.Net Core or in Net.Core in general. The code has been tested in Asp.Net Core 3.1. I have tested out a Generic memory cache and creating middleware for adding items and removing and listing values. Usually you do not want to expose caching to a public api, but perhaps your api resides in a safe(r) intranet zone and you want to cache different objects. This article will teach you the principles upon building a generic memory cache for (asp).net core and to wire up cache functionality to rest api(s). The code of this article is available on Github:

 git clone

We start with our Generic Memory cache. It has some features:
  • The primary feature is to offer generic functionality and STRONGLY TYPED access to the IMemoryCache
  • Strongly typed access means you can use the cache (memory) as a repository and easily add, remove, update and get multiple items in a strongly typed fashion and easily add compound objects (class instances or nested objects, what have you - whatever you want here (as long as it is serializable to Json would be highly suggested in case you want to use the Generic Memory Cache together with REST apis)
  • You add homogenous objects of the same type to a prefixed part of the cache (by prefixed keys) to help avoid collisions in the same process
  • If you add the same key twice, the item will not be added again - you must update instead
  • Additional methods exists for removing, updating and clearing the memory cache.
  • The Generic memory cache wraps IMemoryCache in Asp.Net Core which will do the actual caching in memory on the workstation or server in use for your application.
using Microsoft.Extensions.Caching.Memory; using Microsoft.Extensions.Primitives; using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using System.Threading; namespace SomeAcme.SomeUtilNamespace { /// <summary> /// Thread safe memory cache for generic use - wraps IMemoryCache /// </summary> /// <typeparam name="TCacheItemData">Payload to store in the memory cache</typeparam> /// multiple paralell importing sessions</remarks> public class GenericMemoryCache<TCacheItemData> : IGenericMemoryCache<TCacheItemData> { private readonly string _prefixKey; private readonly int _defaultExpirationInSeconds; private static readonly object _locker = new object(); public GenericMemoryCache(IMemoryCache memoryCache, string prefixKey, int defaultExpirationInSeconds = 0) { defaultExpirationInSeconds = Math.Abs(defaultExpirationInSeconds); //checking if a negative value was passed into the constructor. _prefixKey = prefixKey; Cache = memoryCache; _defaultExpirationInSeconds = defaultExpirationInSeconds; } /// <summary> /// Cache object if direct access is desired. Only allow exposing this for inherited types. /// </summary> protected IMemoryCache Cache { get; } public string PrefixKey(string key) => $"{_prefixKey}_{key}"; //to avoid IMemoryCache collisions with other parts of the same process, each cache key is always prefixed with a set prefix set by the constructor of this class. /// <summary> /// Adds an item to memory cache /// </summary> /// <param name="key"></param> /// <param name="itemToCache"></param> /// <returns></returns> public bool AddItem(string key, TCacheItemData itemToCache) { try { if (!key.StartsWith(_prefixKey)) key = PrefixKey(key); lock (_locker) { if (!Cache.TryGetValue(key, out TCacheItemData existingItem)) { var cts = new CancellationTokenSource(_defaultExpirationInSeconds > 0 ? _defaultExpirationInSeconds * 1000 : -1); var cacheEntryOptions = new MemoryCacheEntryOptions().AddExpirationToken(new CancellationChangeToken(cts.Token)); Cache.Set(key, itemToCache, cacheEntryOptions); return true; } } return false; //Item not added, the key already exists } catch (Exception err) { Debug.WriteLine(err); return false; } } public virtual List<T> GetValues<T>() { lock (_locker) { var values = Cache.GetValues<ICacheEntry>().Where(c => c.Value is T).Select(c => (T)c.Value).ToList(); return values; } } /// <summary> /// Retrieves a cache item. Possible to set the expiration of the cache item in seconds. /// </summary> /// <param name="key"></param> /// <returns></returns> public TCacheItemData GetItem(string key) { try { if (!key.StartsWith(_prefixKey)) key = PrefixKey(key); lock (_locker) { if (Cache.TryGetValue(key, out TCacheItemData cachedItem)) { return cachedItem; } } return default(TCacheItemData); } catch (Exception err) { Debug.WriteLine(err); return default(TCacheItemData); } } public bool SetItem(string key, TCacheItemData itemToCache) { try { if (!key.StartsWith(_prefixKey)) key = PrefixKey(key); lock (_locker) { if (GetItem(key) != null) { AddItem(key, itemToCache); return true; } UpdateItem(key, itemToCache); } return true; } catch (Exception err) { Debug.WriteLine(err); return false; } } /// <summary> /// Updates an item in the cache and set the expiration of the cache item /// </summary> /// <param name="key"></param> /// <param name="itemToCache"></param> /// <returns></returns> public bool UpdateItem(string key, TCacheItemData itemToCache) { if (!key.StartsWith(_prefixKey)) key = PrefixKey(key); lock (_locker) { TCacheItemData existingItem = GetItem(key); if (existingItem != null) { //always remove the item existing before updating RemoveItem(key); } AddItem(key, itemToCache); } return true; } /// <summary> /// Removes an item from the cache /// </summary> /// <param name="key"></param> /// <returns></returns> public bool RemoveItem(string key) { if (!key.StartsWith(_prefixKey)) key = PrefixKey(key); lock (_locker) { if (Cache.TryGetValue(key, out var item)) { if (item != null) { } Cache.Remove(key); return true; } } return false; } public void AddItems(Dictionary<string, TCacheItemData> itemsToCache) { foreach (var kvp in itemsToCache) AddItem(kvp.Key, kvp.Value); } /// <summary> /// Clear all cache keys starting with known prefix passed into the constructor. /// </summary> public void ClearAll() { lock (_locker) { List<string> cacheKeys = Cache.GetKeys<string>().Where(k => k.StartsWith(_prefixKey)).ToList(); foreach (string cacheKey in cacheKeys) { if (cacheKey.StartsWith(_prefixKey)) Cache.Remove(cacheKey); } } } } }
There are different ways of making use of the generic memory cache above. The simplest use-case would be to instantiate it in a Controller and add cache items as wanted. As you can see the Generic Memory cache offers strongly typed access to the memory cache. Lets look at how we can register the Memory Cache as a service too.
// This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) { services.AddControllers(); services.AddMemoryCache(); services.AddSingleton<GenericMemoryCache<WeatherForecast>>(genmen => new GenericMemoryCache<WeatherForecast>(new MemoryCache(new MemoryCacheOptions()), "WEATHER_FORECASTS", 120)); }
In the sample above we register as a singleton (memory is either way shared so making a transient or scoped generic memory cache would be less logical) and register the memory cache above. We can then inject it like this :
private readonly GenericMemoryCache<WeatherForecast> _genericMemoryCache; public WeatherForecastController(ILogger<WeatherForecastController> logger, GenericMemoryCache<WeatherForecast> genericMemoryForecast) { _logger = logger; _genericMemoryCache = genericMemoryForecast; if (_logger != null) { } }
This way of injecting the generic memory cache is cumbersome, since we need to have a more dynamic way of specfifying the type of the memory cache. We could register the type of the generic memory cache to object, but then we loose the strongly typing by boxing the items in the cache to object. Instead, I have looked into defining a custom middleware for working against the generic memory cache. Of course you would in production add some protection against this cache so it cannot be readily available for everyone, such as a token or similar to be added into the REST api calls. The middleware shown next is just a suggestion how we can build up a generic memory cache in core via rest api calls. It should be very handy in case you have consumers / clients that have data they want to store into a cache on-demand. The appliances of this could be endless in an core environment. That is if you would offer such functionality. In many cases, you would otherwise use my GenericMemoryCache more directly where needed and not expose it. But for those who want to see how it can be made available in a REST api, the following middleware offers a suggestion.
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); } .. app.UseGenericMemoryCache(new GenericMemoryCacheOptions { PrefixKey = "volvoer", DefaultExpirationInSeconds = 600 }); ..
We call first the UseGenericMemoryCache to just register the middlware and we initially also set up the PrefixKey to "volvoer" and default expiration in seconds to ten minutes. But we will instead just use Postman to send some rest api calls to build up contents of the cache instead afterwards. The UseMiddleware extension method is used in the extension method that is added to offer this functionality:
using Microsoft.AspNetCore.Builder; namespace SomeAcme.SomeUtilNamespace { public static class GenericMemoryCacheExtensions { public static IApplicationBuilder UseGenericMemoryCache<TItemData>(this IApplicationBuilder builder, GenericMemoryCacheOptions options) where TItemData: class { return builder.UseMiddleware<GenericMemoryCacheMiddleware<TItemData>>(options); } } }
The middleware looks like this (it could be easily extended to cover more functions of the API):
using Microsoft.AspNetCore.Http; using Microsoft.Extensions.Caching.Memory; using Newtonsoft.Json; using System; using System.IO; using System.Text; using System.Threading.Tasks; namespace SomeAcme.SomeUtilNamespace { public class GenericMemoryCacheMiddleware<TCacheItemData> where TCacheItemData: class { private readonly RequestDelegate _next; private readonly string _prefixKey; private readonly int _defaultExpirationTimeInSeconds; public GenericMemoryCacheMiddleware(RequestDelegate next, GenericMemoryCacheOptions options) { if (options == null) { throw new ArgumentNullException(nameof(options)); } _next = next; _prefixKey = options.PrefixKey; _defaultExpirationTimeInSeconds = options.DefaultExpirationInSeconds; } public async Task InvokeAsync(HttpContext context, IMemoryCache memoryCache) { context.Request.EnableBuffering(); //do this to be able to re-read the body multiple times without consuming it. ( core 3.1) if (context.Request.Method.ToLower() == "post") { if (IsDefinedCacheOperation("addtocache", context)) { // Leave the body open so the next middleware can read it. using (var reader = new StreamReader( context.Request.Body, encoding: Encoding.UTF8, detectEncodingFromByteOrderMarks: false, bufferSize: 4096, leaveOpen: true)) { var body = await reader.ReadToEndAsync(); // Do some processing with body if (body != null) { string cacheKey = context.Request.Query["cachekey"].ToString(); if (context.Request.Query.ContainsKey("type")) { var typeArgs = CreateGenericCache(context, memoryCache, out var cache); var payloadItem = JsonConvert.DeserializeObject(body, typeArgs[0]); var addMethod = cache.GetType().GetMethod("AddItem"); if (addMethod != null) { addMethod.Invoke(cache, new[] {cacheKey, payloadItem}); } } else { var cache = new GenericMemoryCache<object>(memoryCache, cacheKey, 0); if (cache != null) { //TODO: implement } } } } // Reset the request body stream position so the next middleware can read it context.Request.Body.Position = 0; } } if (context.Request.Method.ToLower() == "delete") { if (IsDefinedCacheOperation("removeitemfromcache", context)) { var typeArgs = CreateGenericCache(context, memoryCache, out var cache); var removeMethod = cache.GetType().GetMethod("RemoveItem"); string cacheKey = context.Request.Query["cachekey"].ToString(); if (removeMethod != null) { removeMethod.Invoke(cache, new[] { cacheKey }); } } } if (context.Request.Method.ToLower() == "get") { if (IsDefinedCacheOperation("getvaluesfromcache", context)) { var typeArgs = CreateGenericCache(context, memoryCache, out var cache); var getValuesMethod = cache.GetType().GetMethod("GetValues"); if (getValuesMethod != null) { var genericGetValuesMethod = getValuesMethod.MakeGenericMethod(typeArgs); var existingValuesInCache = genericGetValuesMethod.Invoke(cache, null); if (existingValuesInCache != null) { context.Response.ContentType = "application/json"; await context.Response.WriteAsync(JsonConvert.SerializeObject(existingValuesInCache)); } else { context.Response.ContentType = "application/json"; await context.Response.WriteAsync("{}"); //return empty object literal } return; //terminate further processing - return data } } } await _next(context); } private static bool IsDefinedCacheOperation(string cacheOperation, HttpContext context, bool requireType = true) { return context.Request.Query.ContainsKey(cacheOperation) && context.Request.Query.ContainsKey("prefix") && (!requireType || context.Request.Query.ContainsKey("type")); } private static Type[] CreateGenericCache(HttpContext context, IMemoryCache memoryCache, out object cache) { Type genericType = typeof(GenericMemoryCache<>); string cacheitemtype = context.Request.Query["type"].ToString(); string prefix = context.Request.Query["prefix"].ToString(); Type[] typeArgs = {Type.GetType(cacheitemtype)}; Type cacheType = genericType.MakeGenericType(typeArgs); cache = Activator.CreateInstance(cacheType, memoryCache, prefix, 0); return typeArgs; } } }
The middleware above for now supports adding items to the cache and removing them or listing them up. I have used this busines model to test it out:
  namespace GenericMemoryCacheAspNetCore.Models

    public class Car
        public Car()
            NumberOfWheels = 4;

        public string Make { get; set; }
        public string Model { get; set; }
        public int NumberOfWheels { get; set; }


The following requests were tested to add three cars and then delete one and then list them up:
  # add three cars
  POST https://localhost:44391/caching/addcar?addtocache&prefix=volvoer&cachekey=240&type=GenericMemoryCacheAspNetCore.Models.Car,GenericMemoryCacheAspNetCore
  POST https://localhost:44391/caching/addcar?addtocache&prefix=volvoer&cachekey=Amazon&type=GenericMemoryCacheAspNetCore.Models.Car,GenericMemoryCacheAspNetCore
  POST https://localhost:44391/caching/addcar?addtocache&prefix=volvoer&cachekey=Pv&type=GenericMemoryCacheAspNetCore.Models.Car,GenericMemoryCacheAspNetCore
  #remove one
  DELETE https://localhost:44391/caching?removeitemfromcache&prefix=volvoer&cachekey=Amazon&&type=GenericMemoryCacheAspNetCore.Models.Car,GenericMemoryCacheAspNetCore
  # list up the cars in the cache (items)
  GET https://localhost:44391/caching/addcar?getvaluesfromcache&prefix=volvoer&type=GenericMemoryCacheAspNetCore.Models.Car,GenericMemoryCacheAspNetCore
About the POST, I have posted payloads in the body via postman such as this:
    Make: "Volvo",
    Model: "Amazon"
Finally, we can see that we get the cached data in our generic memory cache. As you can see, the REST api specifies the type arguments by specifying the type name with namespaces and after the comma, also the asembly name (fully qualified type name). So this way of building a generic memory cache via rest api is fully feasible in core. However, it should only be used in scenarios where such functionality is desired and the clients can be trusted in some way (or by restricing access to such functionality only to priviledged users via a token or other functionality.) You would of course never allow clients to just send over data to a server's memory cache only to see it bogged down by memory. That was not the purpose of this article. The purpose was to acquaint the reader more with IMemoryCache, Generic Memory cache and middlware in Asp.Net Core. A generic memory cache will give you strongly typed access to memory cache in core and the concepts shown here in .net core should be similar.