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Introduction

ASP.NET Boilerplate provides an abstraction for caching. It internally uses this cache abstraction. While the default implementation uses MemoryCache, it can be implemented and swapped out with any other caching provider. The Abp.RedisCache package implements cache using Redis, for instance (see the "Redis Cache Integration" section below).

ICacheManager

The main interface for caching is ICacheManager. We can inject it and use it to get a cache. Example:

public class TestAppService : ApplicationService
{
    private readonly ICacheManager _cacheManager;

    public TestAppService(ICacheManager cacheManager)
    {
        _cacheManager = cacheManager;
    }

    public Item GetItem(int id)
    {
        //Try to get from cache
        return _cacheManager
                .GetCache("MyCache")
                .Get(id.ToString(), () => GetFromDatabase(id)) as Item;
    }

    public Item GetFromDatabase(int id)
    {
        //... retrieve item from database
    }
}

In this example, we're injecting ICacheManager and getting a cache named MyCache. Cache names are case sensitive, that means "MyCache" and "MYCACHE" are two different caches.

ICache

The ICacheManager.GetCache method returns an ICache. A cache is a singleton (per cache name). It is created the first time it's requested, and then the same cache object is always returned. This way we can share the same cache with the same name in different classes (clients).

In the sample code, we see a simple usage of the ICache.Get method. It has two arguments:

  • key: A unique key (string) of an item in the cache.
  • factory: An action which is called if there is no item with the given key. The Factory method should create and return the actual item. This is not called if the given key is present in the cache.

The ICache interface also has methods like GetOrDefault, Set, Remove and Clear. There are also async versions for all methods.

ITypedCache

The ICache interface uses a string as the key and an object as the value. ITypedCache is a wrapper to ICache to provide a type safe, generic cache. We can use the generic GetCache extension method to get an ITypedCache:

ITypedCache<int, Item> myCache = _cacheManager.GetCache<int, Item>("MyCache");

We can also use the AsTyped extension method to convert an existing ICache instance to ITypedCache.

Configuration

The default cache expiration time is 60 minutes. It's sliding, so if you don't use an item in the cache for 60 minutes, it's automatically removed from the cache. You can configure it for all caches or for a specific cache.

//Configuration for all caches
Configuration.Caching.ConfigureAll(cache =>
{
    cache.DefaultSlidingExpireTime = TimeSpan.FromHours(2);
});

//Configuration for a specific cache
Configuration.Caching.Configure("MyCache", cache =>
{
    cache.DefaultSlidingExpireTime = TimeSpan.FromHours(8);
});

This code should be placed in the PreInitialize method of your module. With this code, "MyCache" will expire in 8 hours while all other cache items will expire in 2 hours.

Your configuration action is called once the cache is first created (on first request). Configuration is not restricted to DefaultSlidingExpireTime only, since the cache object is an ICache, you can use it's properties and methods to freely configure and initialize it.

Entity Caching

While ASP.NET Boilerplate's cache system is for general purposes, there is an EntityCache base class that can help you if you want to cache entities. We can use this base class if we get entities by their Ids and we want to cache them by Id, so as to not query from the database repeatedly. Assume that we have a Person entity like that:

public class Person : Entity
{
    public string Name { get; set; }

    public int Age { get; set; }
}

Assume that we frequently want to get the Name of people while we know their Id. First, we create a class to store cache items:

[AutoMapFrom(typeof(Person))]
public class PersonCacheItem
{
    public string Name { get; set; }
}

Do not directly store entities in the cache, since caching may need to serialize cached objects. Entities may not be serialized, especially if they have navigation properties. That's why we defined a simple (/Pages/Documents/[DTO]Data-Transfer-Objects)) class to store data in the cache. We added the AutoMapFrom attribute since we want to use AutoMapper to automatically convert the Person entities to the PersonCacheItem objects. If we don't use AutoMapper, we should override the MapToCacheItem method of the EntityCache class to manually convert/map it.

While it's not required, we may want to define an interface for our cache class:

public interface IPersonCache : IEntityCache<PersonCacheItem>
{

}

Finally, we can create the cache class to cache Person entities:

public class PersonCache : EntityCache<Person, PersonCacheItem>, IPersonCache, ITransientDependency
{
    public PersonCache(ICacheManager cacheManager, IRepository<Person> repository)
        : base(cacheManager, repository)
    {

    }
}

That's it. Our person cache is ready to use! Cache class can be transient (as in this example) or a singleton. This does not mean the cached data is transient. It's always cached globally and accessed in a thread-safe manner in your application.

Whenever we now need the Name of a person, we can get it from the cache by using the person's Id. Here's an example class that uses the Person cache:

public class MyPersonService : ITransientDependency
{
    private readonly IPersonCache _personCache;

    public MyPersonService(IPersonCache personCache)
    {
        _personCache = personCache;
    }

    public string GetPersonNameById(int id)
    {
        return _personCache[id].Name; //alternative: _personCache.Get(id).Name;
    }
}

We simply injected IPersonCache, got the cache item and then got the Name property.

How EntityCache Works

  • It gets the entity from the repository (the database) in it's first call. It then gets from the cache in subsequent calls.
  • It automatically invalidates a cached entity if this entity is updated or deleted. Thus, it will be retrieved from the database in the next call.
  • It uses IObjectMapper to map an entity to a cache item. IObjectMapper is implemented by the AutoMapper module. You need the AutoMapper module if you are using it. You can override the MapToCacheItem method to manually map an entity to a cache item.
  • It uses the cache class's FullName as a cache name. You can change it by passing a cache name to the base constructor.
  • It's thread-safe.

If you need more complex caching requirements, you can extend EntityCache or create your own solution.

Redis Cache Integration

The default cache manager uses in-memory caches. It can turn in to a problem if you have more than one concurrent web server running the same application. In that case, you may want a distributed/central cache server. You can easily use Redis as your cache server.

First, you need to install the Abp.RedisCache NuGet package to your application (you can install it to your Web project, for example). Then you need to add a DependsOn attribute for the AbpRedisCacheModule and call the UseRedis extension method in the PreInitialize method of your module, as shown below:

//...other namespaces
using Abp.Runtime.Caching.Redis;

namespace MyProject.AbpZeroTemplate.Web
{
    [DependsOn(
        //...other module dependencies
        typeof(AbpRedisCacheModule))]
    public class MyProjectWebModule : AbpModule
    {
        public override void PreInitialize()
        {
            //...other configurations
            
            Configuration.Caching.UseRedis();
        }
        
        //...other code
    }
}

The Abp.RedisCache package uses "localhost" as the connection string by default. You can add a connection string to your config file to override it. Example:

<add name="Abp.Redis.Cache" connectionString="localhost"/>

Also, you can add a setting to appSettings to set the database id of Redis. Example:

<add key="Abp.Redis.Cache.DatabaseId" value="2"/>

Different database ids are useful to create different key spaces (isolated caches) in same server.

The UseRedis method also has an overload that takes an action to directly set option values (this overrides values in the config file).

See the Redis documentation for more information on Redis and it's configuration.

Note: The Redis server should be installed and running to use the Redis cache in ABP.