NHibernate.Caches.Redis

This is a Redis based ICacheProvider for NHibernate written in C# using StackExchange.Redis.

Installation

1. You can install using NuGet: PM> Install-Package NHibernate.Caches.Redis
2. Or build/install from source: msbuild .\build\build.proj and then look inside the bin directory.

Usage

Configure NHibernate to use the custom cache provider:

<property name="cache.use_second_level_cache">true</property>
<property name="cache.use_query_cache">true</property>
<property name="cache.provider_class">NHibernate.Caches.Redis.RedisCacheProvider, 
    NHibernate.Caches.Redis</property>

Set the ConnectionMultiplexer on the RedisCacheProvider before creating your ISessionFactory:

// Or use your IoC container to wire this up.
var connectionMultiplexer = ConnectionMultiplexer.Connect("localhost:6379");
RedisCacheProvider.SetConnectionMultiplexer(connectionMultiplexer);

using (var sessionFactory = ...)
{
    // ...
}

// When your application exits:
connectionMultiplexer.Dispose();

Check out the NHibernate.Caches.Redis.Sample project to learn more.

Options

You can customize certain behavior with the RedisCacheProvider.SetOptions(options) method. For example, you can control how objects are serialized into Redis. Here is a JSON.NET ICacheSerializer implementation. Once added to your project, you can then configure the options:

var options = new RedisCacheProviderOptions()
{
    Serializer = new NhJsonCacheSerializer()
};
RedisCacheProvider.SetOptions(options);

Cache Region Configuration

NOTE: XML-based cache configuration (app.config/web.config) was removed in version 3.0.

Using the CacheConfigurations option, you can customize each region:

RedisCacheProvider.SetOptions(new RedisCacheProviderOptions()
{
    Serializer = new NetDataContractCacheSerializer(),
    CacheConfigurations = new[]
    {
        new RedisCacheConfiguration("BlogPost") { Expiration = TimeSpan.FromSeconds(9) }
    }
});

Exception Handling

You may require that NHibernate gracefully continue to the database as if it missed the cache when an exception occurs. For example, imagine if you are using NHibernate in a web project and your Redis server is unavailable. You may not want NHibernate to continue to timeout for every NHibernate operation. You could do something similar to this:

public class RequestRecoveryRedisCache : RedisCache
{
    public const string SkipNHibernateCacheKey = "__SkipNHibernateCache__";

    public RequestRecoveryRedisCache(string regionName, IDictionary<string, string> properties, RedisCacheElement element, ConnectionMultiplexer connectionMultiplexer, RedisCacheProviderOptions options)
        : base(regionName, properties, element, connectionMultiplexer, options)
    {

    }

    public override object Get(object key)
    {
        if (HasFailedForThisHttpRequest()) return null;
        return base.Get(key);
    }

    public override void Put(object key, object value)
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Put(key, value);
    }

    public override void Remove(object key)
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Remove(key);
    }

    public override void Clear()
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Clear();
    }

    public override void Destroy()
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Destroy();
    }

    public override void Lock(object key)
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Lock(key);
    }

    public override void Unlock(object key)
    {
        if (HasFailedForThisHttpRequest()) return;
        base.Unlock(key);
    }

    private bool HasFailedForThisHttpRequest()
    {
        return HttpContext.Current.Items.Contains(SkipNHibernateCacheKey);
    }
}

public class RequestRecoveryRedisCacheProvider : RedisCacheProvider
{
    protected override RedisCache BuildCache(string regionName, IDictionary<string, string> properties, RedisCacheElement configElement, ConnectionMultiplexer connectionMultiplexer, RedisCacheProviderOptions options)
    {
        options.OnException = (e) =>
        {
            HttpContext.Current.Items[RequestRecoveryRedisCache.SkipNHibernateCacheKey] = true;
        };

        return new RequestRecoveryRedisCache(regionName, properties, configElement, connectionMultiplexer, options);
    }
}

Then, use RequestRecoveryRedisCacheProvider in your web.config settings.

StackExchange.Redis and Strong Naming

If one of your other libraries references StackExchange.Redis.StrongName, and you're having trouble building, you can use a build alias on the strongly named reference to get things to play nice together.

Changelog

3.0.0

• IMPORTANT: Updating to this release will cause all of your caches to be invalidated because of changes to the cache keys.
• The generational approach to keeping track of keys has been removed in favor of using Lua scripts. This means better performance but will require Redis >= 2.6.12 to support Lua scripts. This also means the cache keys are more simple: NHibernate-Cache:<region_name>:<key>.
• Cache region configuration has been moved from XML to code. A RedisCacheConfiguration can be created and set on the RedisCacheProviderOptions.CacheConfigurations option.
• Lock values are now created by an ILockValueFactory instead of a Func<string>.
• Add customization of the acquire-lock retry strategy (IAcquireLockRetryStrategy). The default retry strategy has been changed to use an exponential backoff.
• Allow configuring the timeout when acquiring a lock. Use the RedisCacheConfiguration.AcquireLockTimeout property. It's then available to the IAcquireLockRetryStrategy.
• Allow getting an item from the cache to reset the expiration (sliding expiration). Use the RedisCacheConfiguration.SlidingExpiration property. By default, no sliding expiration occurs.
• Rename RedisCacheExceptionEventArgs to ExceptionEventArgs and convert OnException to an event: RedisCacheProviderOptions.Exception.
• Add more context (region name and method name) to the ExceptionEventArgs.
• Add LockFailed and UnlockFailed events to RedisCacheProviderOptions for handling when locking/unlocking fails (other than exceptions).

2.0.0

• Switch the Redis library to StackExchange.Redis because of licensing changes with ServiceStack.Redis. This obviously causes a few breaking changes with the constructors.
• Introduce RedisCacheProvider.SetOptions (so that, for example, you don't need to subclass to override OnException).
• Allow the serializer to be customized by implementing ICacheSerializer and setting the Serializer on the options. The default serializer uses the NetDataContractSerializer.
• Customize which database the Redis connection uses with the Database option.
• The cache key no longer duplicates the region prefix. In previous versions, caching an object with the type MyApp.Models.Blog and a region prefix of v2 would use the key v2:NHibernate-Cache:v2.MyApp.Models.Blog:keys. The key is now v2:NHibernate-Cache:MyApp.Models.Blog:keys.
• Allow the lock value to be customized. This is useful if you want to store information such as what machine/process generated the lock to help with debugging.
• Wrap exceptions that can occur in RedisCache with RedisCacheException.

1.3.0

• Add the OnException method for sub-classing the cache client and handling exceptions.

1.2.1

• Update ServiceStack.Redis to 3.9.55.

1.2.0

• Allow the provider to gracefully continue when Redis is unavailable.
• Fix infinite loop when data in Redis was cleared.

1.1.0

• Added configuration section for customizing the cache regions.
• Added sample project.

1.0.0

• Initial release.

Contributors

@MattiasJakobsson and @Tazer for helping switch over to StackExchange.Redis.

Happy caching!