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Caching

ABP Framework extends the ASP.NET Core distributed cache.

Installation

This package is already installed by default with the application startup template. So, most of the time, you don't need to install it manually.

Volo.Abp.Caching is the main package of the caching system. You can install it a project using the add-package command of the ABP CLI:

abp add-package Volo.Abp.Caching

You need to run this command on a command line terminal in a folder containing a csproj file (see other options to install).

Usage

`IDistributedCache` Interface

ASP.NET Core defines the IDistributedCache interface to get/set the cache values. But it has some difficulties:

It works with byte arrays rather than .NET objects. So, you need to serialize/deserialize the objects you need to cache.
It provides a single key pool for all cache items, so;
- You need to care about the keys to distinguish different type of objects.
- You need to care about the cache items of different tenants in a multi-tenant system.

IDistributedCache is defined in the Microsoft.Extensions.Caching.Abstractions package. That means it is not only usable for ASP.NET Core applications, but also available to any type of applications.

Default implementation of the IDistributedCache interface is the MemoryDistributedCache which works in-memory. See ASP.NET Core's documentation to see how to switch to Redis or another cache provider. Also, see the Redis Cache document if you want to use the Redis as the distributed cache server.

See ASP.NET Core's distributed caching document for more information.

`IDistributedCache<TCacheItem>` Interface

ABP framework defines the generic IDistributedCache<TCacheItem> interface in the Volo.Abp.Caching package. TCacheItem is the type of the object stored in the cache.

IDistributedCache<TCacheItem> solves the difficulties explained above;

It internally serializes/deserializes the cached objects. Uses JSON serialization by default, but can be overridden by replacing the IDistributedCacheSerializer service in the dependency injection system.
It automatically adds a cache name prefix to the cache keys based on the object type stored in the cache. Default cache name is the full name of the cache item class (CacheItem postfix is removed if your cache item class ends with it). You can use the CacheName attribute on the cache item class to set the cache name.
It automatically adds the current tenant id to the cache key to distinguish cache items for different tenants (if your application is multi-tenant). Define IgnoreMultiTenancy attribute on the cache item class to disable this if you want to share the cached objects among all tenants in a multi-tenant application.
Allows to define a global cache key prefix per application, so different applications can use their isolated key pools in a shared distributed cache server.
It can tolerate errors wherever possible and bypasses the cache. This is useful when you have temporary problems on the cache server.
It has methods like GetManyAsync and SetManyAsync which significantly improve the performance on batch operations.

Example: Store Book names and prices in the cache

namespace MyProject
{
    public class BookCacheItem
    {
        public string Name { get; set; }

        public float Price { get; set; }
    }
}

You can inject and use the IDistributedCache<BookCacheItem> service to get/set BookCacheItem objects:

using System;
using System.Threading.Tasks;
using Microsoft.Extensions.Caching.Distributed;
using Volo.Abp.Caching;
using Volo.Abp.DependencyInjection;

namespace MyProject
{
    public class BookService : ITransientDependency
    {
        private readonly IDistributedCache<BookCacheItem> _cache;

        public BookService(IDistributedCache<BookCacheItem> cache)
        {
            _cache = cache;
        }

        public async Task<BookCacheItem> GetAsync(Guid bookId)
        {
            return await _cache.GetOrAddAsync(
                bookId.ToString(), //Cache key
                async () => await GetBookFromDatabaseAsync(bookId),
                () => new DistributedCacheEntryOptions
                {
                    AbsoluteExpiration = DateTimeOffset.Now.AddHours(1)
                }
            );
        }

        private Task<BookCacheItem> GetBookFromDatabaseAsync(Guid bookId)
        {
            //TODO: get from database
        }
    }
}

This sample service uses the GetOrAddAsync() method to get a book item from the cache. GetOrAddAsync is an additional method that was added by the ABP Framework to the standard ASP.NET Core distributed cache methods.
If the book was not found in the cache, it calls the factory method (GetBookFromDatabaseAsync in this case) to retrieve the book item from the original source.
GetOrAddAsync optionally gets a DistributedCacheEntryOptions which can be used to set the lifetime of the cached item.

IDistributedCache<BookCacheItem> supports the same methods of the ASP.NET Core's standard IDistributedCache interface, so you can refer it's documentation.

`IDistributedCache<TCacheItem, TCacheKey>` Interface

IDistributedCache<TCacheItem> interface assumes that the type of your cache key is string (so, you need to manually convert your key to string if you need to use a different kind of cache key). While this is not a big deal, IDistributedCache<TCacheItem, TCacheKey> can be used when your cache key type is not string.

Example: Store Book names and prices in the cache

using Volo.Abp.Caching;

namespace MyProject
{
    [CacheName("Books")]
    public class BookCacheItem
    {
        public string Name { get; set; }

        public float Price { get; set; }
    }
}

This example uses the CacheName attribute for the BookCacheItem class to set the cache name.

You can inject and use the IDistributedCache<BookCacheItem, Guid> service to get/set BookCacheItem objects:

using System;
using System.Threading.Tasks;
using Microsoft.Extensions.Caching.Distributed;
using Volo.Abp.Caching;
using Volo.Abp.DependencyInjection;

namespace MyProject
{
    public class BookService : ITransientDependency
    {
        private readonly IDistributedCache<BookCacheItem, Guid> _cache;

        public BookService(IDistributedCache<BookCacheItem, Guid> cache)
        {
            _cache = cache;
        }

        public async Task<BookCacheItem> GetAsync(Guid bookId)
        {
            return await _cache.GetOrAddAsync(
                bookId, //Guid type used as the cache key
                async () => await GetBookFromDatabaseAsync(bookId),
                () => new DistributedCacheEntryOptions
                {
                    AbsoluteExpiration = DateTimeOffset.Now.AddHours(1)
                }
            );
        }
        private Task<BookCacheItem> GetBookFromDatabaseAsync(Guid bookId)
        {
            //TODO: get from database
        }
    }
}

This sample service uses the GetOrAddAsync() method to get a book item from the cache.
Since cache explicitly implemented as using Guid as cache key, Guid value passed to _cache_GetOrAddAsync() method.

Complex Types as the Cache Key

IDistributedCache<TCacheItem, TCacheKey> internally uses ToString() method of the key object to convert it to a string. If you need to use a complex object as the cache key, you need to override ToString method of your class.

An example class that is used as a cache key:

public class UserInOrganizationCacheKey
{
    public Guid UserId { get; set; }
    
    public Guid OrganizationId { get; set; }
    
    //Builds the cache key
    public override string ToString()
    {
        return $"{UserId}_{OrganizationId}";
    }
}

Example usage:

public class BookService : ITransientDependency
{
    private readonly IDistributedCache<UserCacheItem, UserInOrganizationCacheKey> _cache;

    public BookService(
        IDistributedCache<UserCacheItem, UserInOrganizationCacheKey> cache)
    {
        _cache = cache;
    }
    
    ...
}

Configuration

AbpDistributedCacheOptions

AbpDistributedCacheOptions is the main options class to configure the caching.

Example: Set the cache key prefix for the application

Configure<AbpDistributedCacheOptions>(options =>
{
    options.KeyPrefix = "MyApp1";
});

Write that code inside the ConfigureServices method of your module class.

Available Options

HideErrors (bool, default: true): Enables/disables hiding the errors on writing/reading values from the cache server.
KeyPrefix (string, default: null): If your cache server is shared by multiple applications, you can set a prefix for the cache keys for your application. In this case, different applications can not overwrite each other's cache items.
GlobalCacheEntryOptions (DistributedCacheEntryOptions): Used to set default distributed cache options (like AbsoluteExpiration and SlidingExpiration) used when you don't specify the options while saving cache items. Default value uses the SlidingExpiration as 20 minutes.

Error Handling

When you design a cache for your objects, you typically try to get the value from cache first. If not found in the cache, you query the object from the original source. It may be located in a database or may require to perform an HTTP call to a remote server.

In most cases, you want to tolerate the cache errors; If you get error from the cache server you don't want to cancel the operation. Instead, you silently hide (and log) the error and query from the original source. This is what the ABP Framework does by default.

ABP's Distributed Cache handle, log and hide errors by default. There is an option to change this globally (see the options below).

In addition, all of the IDistributedCache<TCacheItem> (and IDistributedCache<TCacheItem, TCacheKey>) methods have an optional hideErrors parameter, which is null by default. The global value is used if this parameter left as null, otherwise you can decide to hide or throw the exceptions for individual method calls.

Batch Operations

ABP's distributed cache interfaces provide methods to perform batch methods those improves the performance when you want to batch operation multiple cache items in a single method call.

SetManyAsync and SetMany methods can be used to set multiple values to the cache.
GetManyAsync and GetMany methods can be used to retrieve multiple values from the cache.
GetOrAddManyAsync and GetOrAddMany methods can be used to retrieve multiple values and set missing values from the cache
RefreshManyAsync and RefreshMany methods can be used to resets the sliding expiration timeout of multiple values from the cache
RemoveManyAsync and RemoveMany methods can be used to remove multiple values from the cache

These are not standard methods of the ASP.NET Core caching. So, some providers may not support them. They are supported by the ABP Redis Cache integration package. If the provider doesn't support, it fallbacks to SetAsync and GetAsync ... methods (called once for each item).

Advanced Topics

Unit Of Work Level Cache

Distributed cache service provides an interesting feature. Assume that you've updated the price of a book in the database, then set the new price to the cache, so you can use the cached value later. What if you have an exception after setting the cache and you rollback the transaction that updates the price of the book? In this case, cache value will be incorrect.

IDistributedCache<..> methods gets an optional parameter, named considerOuw, which is false by default. If you set it to true, then the changes you made for the cache are not actually applied to the real cache store, but associated with the current unit of work. You get the value you set in the same unit of work, but the changes are applied only if the current unit of work succeed.

IDistributedCacheSerializer

IDistributedCacheSerializer service is used to serialize and deserialize the cache items. Default implementation is the Utf8JsonDistributedCacheSerializer class that uses IJsonSerializer service to convert objects to JSON and vice verse. Then it uses UTC8 encoding to convert the JSON string to a byte array which is accepted by the distributed cache.

You can replace this service by your own implementation if you want to implement your own serialization logic.

IDistributedCacheKeyNormalizer

IDistributedCacheKeyNormalizer is implemented by the DistributedCacheKeyNormalizer class by default. It adds cache name, application cache prefix and current tenant id to the cache key. If you need a more advanced key normalization, you can replace this service by your own implementation.

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