Sunday, 27 September 2020

Generic Memory Cache for .Net Core

The following sample code shows how to create a Generic Memory Cache for Asp.Net Core and .Net Core. This allows you to cache specific items defined by a TCacheItemData type argument, i.e. caching same type of data such as instances of a class, or arrays of instances. First off, add the following Nuget package: Install-Package System.Runtime.Caching This should add the necessary cache classes for .Net Core. Inside your .csproj you should see something like:
    
Over to the implementation. Since a memory cache is shared by possibly other applications, it is important to prefix your cached contents, i.e. prefix the the keys. This makes it easier to barrier the memory cache. Note though that some barriering is done accross processes of course, this is just to make it easier within your application and running process to group the cached elements with a prefix key used for the generic memory cache operations. Now over to the implementation.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.Caching;

namespace SomeAcme.SomeUtilNamespace
{
    /// <summary>
    /// Thread safe memory cache for generic use
    /// </summary>
    /// <typeparam name="TCacheItemData">Payload to store in the memory cache</typeparam>
    /// <remarks>Uses MemoryCache.Default which defaults to an in-memory cache. All cache items are prefixed with an 'import cache session guid' to compartmentalize
    /// multiple paralell importing sessions</remarks>
    public class GenericMemoryCache<TCacheItemData> where TCacheItemData : class
    {
        private readonly string _prefixKey;
        private readonly ObjectCache _cache;
        private readonly CacheItemPolicy _cacheItemPolicy;

        public GenericMemoryCache(string prefixKey, int defaultExpirationInSeconds = 0)
        {
            defaultExpirationInSeconds = Math.Abs(defaultExpirationInSeconds); //checking if a negative value was passed into the constructor.

            _prefixKey = prefixKey;
            _cache = MemoryCache.Default;
            _cacheItemPolicy = defaultExpirationInSeconds == 0
                ? new CacheItemPolicy { Priority = CacheItemPriority.NotRemovable }
                : new CacheItemPolicy
                { AbsoluteExpiration = DateTime.Now.AddSeconds(Math.Abs(defaultExpirationInSeconds)) };
        }

        /// <summary>
        /// Cache object if direct access is desired
        /// </summary>
        public ObjectCache Cache => _cache;

        public string PrefixKey(string key) => $"{_prefixKey}_{key}";


        /// <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);

                var cacheItem = new CacheItem(key, itemToCache);
                _cache.Add(cacheItem, _cacheItemPolicy);
                return true;
            }
            catch (Exception err)
            {
                Debug.WriteLine(err);
                return false;
            }
        }

        public virtual List<T> GetValues<T>()
        {
            List<T> list = new List<T>();
            IDictionaryEnumerator cacheEnumerator = (IDictionaryEnumerator)((IEnumerable)_cache).GetEnumerator();

            while (cacheEnumerator.MoveNext())
            {
                if (cacheEnumerator.Key == null)
                    continue;
                if (cacheEnumerator.Key.ToString().StartsWith(_prefixKey))
                    list.Add((T)cacheEnumerator.Value);
            }
            return list;
        }

        /// <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);
                if (_cache.Contains(key))
                {
                    CacheItem cacheItem = _cache.GetCacheItem(key);
                    object cacheItemValue = cacheItem?.Value;
                    UpdateItem(key, cacheItemValue as TCacheItemData);
                    TCacheItemData item = _cache.Get(key) as TCacheItemData;
                    return item;
                }
                return null;
            }
            catch (Exception err)
            {
                Debug.WriteLine(err);
                return null;
            }
        }

        public bool SetItem(string key, TCacheItemData itemToCache)
        {
            try
            {
                if (!key.StartsWith(_prefixKey))
                    key = PrefixKey(key);
                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);
            CacheItem cacheItem = _cache.GetCacheItem(key);
            if (cacheItem != null)
            {
                cacheItem.Value = itemToCache;
                _cache.Set(key, itemToCache, _cacheItemPolicy);
            }
            else
            {
                //if we cant find the cache item, just set the cache directly
                _cache.Set(key, itemToCache, _cacheItemPolicy);

            }
              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);

            if (_cache.Contains(key))
            {
                _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()
        {
            var cacheKeys = _cache.Select(kvp => kvp.Key).ToList();
            foreach (string cacheKey in cacheKeys)
            {
                if (cacheKey.StartsWith(_prefixKey))
                    _cache.Remove(cacheKey);
            }
        }

    }
}




Friday, 10 July 2020

Adding live reloads developing Asp.Net Mvc Core razor views

To add live reloading when developing Asp.Net Core Views, it is recommended to upgrade to .Net Core 3.1. This makes it easier to add in the Nuget package for recompilation. In case you have a .Net Core 2 app, follow the MSDN guide here: https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.1&tabs=visual-studio After the app runs as .Net Core 3.1, run the following (procedure below is tested okay with VS 2019 and Chrome as the browser 'linked' to the reloading: Edit the .csproj file by selecting the project and right clicking and selecting Edit project file in VS 2019. Past in these two Nuget package references and run dotnet restore, then dotnet build and finally dotnet run.

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation" Version="3.1.5" />
    <PackageReference Include="Microsoft.VisualStudio.Web.BrowserLink" Version="2.2.0" />
  </ItemGroup>

The runtime compilation and Browserlink should both be added. The first will rebuild your edited razor views (cshtml) and BrowserLink reloads your browser while debugging, after the razor view is updated. Also download this Visual Studio Extension, "Browser reload on save": https://marketplace.visualstudio.com/items?itemName=MadsKristensen.BrowserReloadonSave You will have to close all Visual Studio processes to start installing Mad Kristensen's browser extension. In your Startup class you should inside ConfigureServices add these two lines, specifying AddRazorRunitmeCompilation:
        services.AddRazorPages().AddRazorRuntimeCompilation();
        services.AddControllersWithViews().AddRazorRuntimeCompilation();
And finally at the top of the Configure method in the Startup class add in BrowserLink. Note, add this at the top of the Configure method such that the pipeline is adding BrowserLink correct.
  if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseBrowserLink();
            }
Now, just start up your app with F5 and start editing a razor file. If all was set up correct, you should now see your razor view reload in the Browser. This makes it easier to edit and adjust razor views!

Sunday, 28 June 2020

Adding Bootstrap 4 to Asp.Net Core MVC solution

To add Bootstrap 4 or newer to an Asp.NET Core MVC Solution, you can do this in the following manner if you use Visual Studio 2019 and .Net Core 3.1. Or at least have access to the 'Manage Client-side Libraries' functionality. Bootstrap is not supported in Nuget and definately not for .Net Core apps, so you need to add it manually using this. The Manage client-side libaries in Visual Studio adds a libman.json file. This is the Library Manager json file, similar to NPM based solutions package.json. Now add the following into libman.json:

{
  "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"
      ]
    }
  ]
}

This adds Bootstrap 4.2.1 and Jquery 3.3.1 into wwwroot lib folders for each library. Now in your _Layout.cshtml file (or the file you use as your Layout file), just drag bootstrap.min.css file and bootstrap.bundle.js files into that razor file. After you restart the solution, you should have Bootstrap 4 available into your Asp.Net Core MVC app! And if you want to add client side libraries using a GUI, select your project and choose then via right click Add->Client side library. Here you can search for client side libraries.