How can I cache objects in ASP.NET MVC?

Question

I\'d like to cache objects in ASP.NET MVC. I have a BaseController that I want all Controllers to inherit from. In the BaseController there is a User

Answer 1

You can still use the cache (shared among all responses) and session (unique per user) for storage.

I like the following "try get from cache/create and store" pattern (c#-like pseudocode):

public static class CacheExtensions
{
  public static T GetOrStore<T>(this Cache cache, string key, Func<T> generator)
  {
    var result = cache[key];
    if(result == null)
    {
      result = generator();
      cache[key] = result;
    }
    return (T)result;
  }
}

you'd use this like so:

var user = HttpRuntime
              .Cache
              .GetOrStore<User>(
                 $"User{_userId}", 
                 () => Repository.GetUser(_userId));

You can adapt this pattern to the Session, ViewState (ugh) or any other cache mechanism. You can also extend the ControllerContext.HttpContext (which I think is one of the wrappers in System.Web.Extensions), or create a new class to do it with some room for mocking the cache.

Answer 2

@njappboy: Nice implementation. I would only defer the Generator( ) invocation until the last responsible moment. thus you can cache method invocations too.

/// <summary>
/// Allows Caching of typed data
/// </summary>
/// <example><![CDATA[
/// var user = HttpRuntime
///   .Cache
///   .GetOrStore<User>(
///      string.Format("User{0}", _userId), 
///      () => Repository.GetUser(_userId));
///
/// ]]></example>
/// <typeparam name="T"></typeparam>
/// <param name="Cache">calling object</param>
/// <param name="Key">Cache key</param>
/// <param name="Generator">Func that returns the object to store in cache</param>
/// <returns></returns>
/// <remarks>Uses a default cache expiration period as defined in <see cref="CacheExtensions.DefaultCacheExpiration"/></remarks>
public static T GetOrStore<T>( this Cache Cache, string Key, Func<T> Generator )
{
    return Cache.GetOrStore( Key, Generator, DefaultCacheExpiration );
}

/// <summary>
/// Allows Caching of typed data
/// </summary>
/// <example><![CDATA[
/// var user = HttpRuntime
///   .Cache
///   .GetOrStore<User>(
///      string.Format("User{0}", _userId), 
///      () => Repository.GetUser(_userId));
///
/// ]]></example>
/// <typeparam name="T"></typeparam>
/// <param name="Cache">calling object</param>
/// <param name="Key">Cache key</param>
/// <param name="Generator">Func that returns the object to store in cache</param>
/// <param name="ExpireInMinutes">Time to expire cache in minutes</param>
/// <returns></returns>
public static T GetOrStore<T>( this Cache Cache, string Key, Func<T> Generator, double ExpireInMinutes )
{
    var Result = Cache [ Key ];

    if( Result == null )
    {
        lock( Sync )
        {
            if( Result == null )
            {
                Result = Generator( );
                Cache.Insert( Key, Result, null, DateTime.Now.AddMinutes( ExpireInMinutes ), Cache.NoSlidingExpiration );
            }
        }
    }

    return ( T ) Result;
}

Answer 3

If you want it cached for the length of the request, put this in your controller base class:

public User User {
    get {
        User _user = ControllerContext.HttpContext.Items["user"] as User;

        if (_user == null) {
            _user = _repository.Get<User>(id);
            ControllerContext.HttpContext.Items["user"] = _user;
        }

        return _user;
    }
}

If you want to cache for longer, use the replace the ControllerContext call with one to Cache[]. If you do choose to use the Cache object to cache longer, you'll need to use a unique cache key as it will be shared across requests/users.

Answer 4

A couple of the other answers here don't deal with the following:

• cache stampede
• double check lock

This could lead to the generator (which could take a long time) running more than once in different threads.

Here's my version that shouldn't suffer from this problem:

// using System;
// using System.Web.Caching;

// https://stackoverflow.com/a/42443437
// Usage: HttpRuntime.Cache.GetOrStore("myKey", () => GetSomethingToCache());

public static class CacheExtensions
{
    private static readonly object sync = new object();
    private static TimeSpan defaultExpire = TimeSpan.FromMinutes(20);

    public static T GetOrStore<T>(this Cache cache, string key, Func<T> generator) =>
        cache.GetOrStore(key, generator, defaultExpire);

    public static T GetOrStore<T>(this Cache cache, string key, Func<T> generator, TimeSpan expire)
    {
        var result = cache[key];
        if (result == null)
        {
            lock (sync)
            {
                result = cache[key];
                if (result == null)
                {
                    result = generator();
                    cache.Insert(key, result, null, DateTime.UtcNow.AddMinutes(expire.TotalMinutes), Cache.NoSlidingExpiration);
                }
            }
        }
        return (T)result;
    }
}

Answer 5

Implementation with a minimal cache locking. The value stored in the cache is wrapped in a container. If the value is not in the cache, then the value container is locked. The cache is locked only during the creation of the container.

public static class CacheExtensions
{
    private static object sync = new object();

    private class Container<T>
    {
        public T Value;
    }

    public static TValue GetOrStore<TValue>(this Cache cache, string key, Func<TValue> create, TimeSpan slidingExpiration)
    {
        return cache.GetOrStore(key, create, Cache.NoAbsoluteExpiration, slidingExpiration);
    }

    public static TValue GetOrStore<TValue>(this Cache cache, string key, Func<TValue> create, DateTime absoluteExpiration)
    {
        return cache.GetOrStore(key, create, absoluteExpiration, Cache.NoSlidingExpiration);
    }

    public static TValue GetOrStore<TValue>(this Cache cache, string key, Func<TValue> create, DateTime absoluteExpiration, TimeSpan slidingExpiration)
    {
        return cache.GetOrCreate(key, x => create());
    }

    public static TValue GetOrStore<TValue>(this Cache cache, string key, Func<string, TValue> create, DateTime absoluteExpiration, TimeSpan slidingExpiration)
    {
        var instance = cache.GetOrStoreContainer<TValue>(key, absoluteExpiration, slidingExpiration);
        if (instance.Value == null)
            lock (instance)
                if (instance.Value == null)
                    instance.Value = create(key);

        return instance.Value;
    }

    private static Container<TValue> GetOrStoreContainer<TValue>(this Cache cache, string key, DateTime absoluteExpiration, TimeSpan slidingExpiration)
    {
        var instance = cache[key];
        if (instance == null)
            lock (cache)
            {
                instance = cache[key];
                if (instance == null)
                {
                    instance = new Container<TValue>();

                    cache.Add(key, instance, null, absoluteExpiration, slidingExpiration, CacheItemPriority.Default, null);
                }
            }

        return (Container<TValue>)instance;
    }
}

Answer 6

I took Will's answer and modified it to make the CacheExtensions class static and to suggest a slight alteration in order to deal with the possibility of Func<T> being null :

public static class CacheExtensions
{

    private static object sync = new object();
    public const int DefaultCacheExpiration = 20;

    /// <summary>
    /// Allows Caching of typed data
    /// </summary>
    /// <example><![CDATA[
    /// var user = HttpRuntime
    ///   .Cache
    ///   .GetOrStore<User>(
    ///      string.Format("User{0}", _userId), 
    ///      () => Repository.GetUser(_userId));
    ///
    /// ]]></example>
    /// <typeparam name="T"></typeparam>
    /// <param name="cache">calling object</param>
    /// <param name="key">Cache key</param>
    /// <param name="generator">Func that returns the object to store in cache</param>
    /// <returns></returns>
    /// <remarks>Uses a default cache expiration period as defined in <see cref="CacheExtensions.DefaultCacheExpiration"/></remarks>
    public static T GetOrStore<T>( this Cache cache, string key, Func<T> generator ) {
        return cache.GetOrStore( key, (cache[key] == null && generator != null) ? generator() : default( T ), DefaultCacheExpiration );
    }


    /// <summary>
    /// Allows Caching of typed data
    /// </summary>
    /// <example><![CDATA[
    /// var user = HttpRuntime
    ///   .Cache
    ///   .GetOrStore<User>(
    ///      string.Format("User{0}", _userId), 
    ///      () => Repository.GetUser(_userId));
    ///
    /// ]]></example>
    /// <typeparam name="T"></typeparam>
    /// <param name="cache">calling object</param>
    /// <param name="key">Cache key</param>
    /// <param name="generator">Func that returns the object to store in cache</param>
    /// <param name="expireInMinutes">Time to expire cache in minutes</param>
    /// <returns></returns>
    public static T GetOrStore<T>( this Cache cache, string key, Func<T> generator, double expireInMinutes ) {
        return cache.GetOrStore( key,  (cache[key] == null && generator != null) ? generator() : default( T ), expireInMinutes );
    }


    /// <summary>
    /// Allows Caching of typed data
    /// </summary>
    /// <example><![CDATA[
    /// var user = HttpRuntime
    ///   .Cache
    ///   .GetOrStore<User>(
    ///      string.Format("User{0}", _userId),_userId));
    ///
    /// ]]></example>
    /// <typeparam name="T"></typeparam>
    /// <param name="cache">calling object</param>
    /// <param name="key">Cache key</param>
    /// <param name="obj">Object to store in cache</param>
    /// <returns></returns>
    /// <remarks>Uses a default cache expiration period as defined in <see cref="CacheExtensions.DefaultCacheExpiration"/></remarks>
    public static T GetOrStore<T>( this Cache cache, string key, T obj ) {
        return cache.GetOrStore( key, obj, DefaultCacheExpiration );
    }

    /// <summary>
    /// Allows Caching of typed data
    /// </summary>
    /// <example><![CDATA[
    /// var user = HttpRuntime
    ///   .Cache
    ///   .GetOrStore<User>(
    ///      string.Format("User{0}", _userId), 
    ///      () => Repository.GetUser(_userId));
    ///
    /// ]]></example>
    /// <typeparam name="T"></typeparam>
    /// <param name="cache">calling object</param>
    /// <param name="key">Cache key</param>
    /// <param name="obj">Object to store in cache</param>
    /// <param name="expireInMinutes">Time to expire cache in minutes</param>
    /// <returns></returns>
    public static T GetOrStore<T>( this Cache cache, string key, T obj, double expireInMinutes ) {
        var result = cache[key];

        if ( result == null ) {

            lock ( sync ) {
                result = cache[key];
                if ( result == null ) {
                    result = obj != null ? obj : default( T );
                    cache.Insert( key, result, null, DateTime.Now.AddMinutes( expireInMinutes ), Cache.NoSlidingExpiration );
                }
            }
        }

        return (T)result;

    }

}

I would also consider taking this a step further to implement a testable Session solution that extends the System.Web.HttpSessionStateBase abstract class.

public static class SessionExtension
{
    /// <summary>
    /// 
    /// </summary>
    /// <example><![CDATA[
    /// var user = HttpContext
    ///   .Session
    ///   .GetOrStore<User>(
    ///      string.Format("User{0}", _userId), 
    ///      () => Repository.GetUser(_userId));
    ///
    /// ]]></example>
    /// <typeparam name="T"></typeparam>
    /// <param name="cache"></param>
    /// <param name="key"></param>
    /// <param name="generator"></param>
    /// <returns></returns>
    public static T GetOrStore<T>( this HttpSessionStateBase session, string name, Func<T> generator ) {

        var result = session[name];
        if ( result != null )
            return (T)result;

        result = generator != null ? generator() : default( T );
        session.Add( name, result );
        return (T)result;
    }

}