NHibernate.Caches.Redis

This is a Redis based ICacheProvider for NHibernate written in C# using ServiceStack.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 IRedisClientsManager (pooled, basic, etc) on the RedisCacheProvider before creating your ISessionFactory:

// Or use your IoC container to wire this up.
var clientManager = new PooledRedisClientManager("localhost:6379");
RedisCacheProvider.SetClientManager(clientManager);

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

clientManager.Dispose();

Configuration

Inside of the app/web.config, a custom configuration section can be added to configure each cache region:

<configSections>
  <section name="nhibernateRedisCache" type="NHibernate.Caches.Redis.RedisCacheProviderSection, NHibernate.Caches.Redis" />
</configSections>

<nhibernateRedisCache>
  <caches>
    <cache region="BlogPost" expiration="900" />
  </caches>
</nhibernateRedisCache>

Exception Handling

You may require that we gracefully continue to the database as if we "missed" the cache if an exception occurs. By default, this is what happens.

However, there is also the need of advanced exception handling scenarios. 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. Therefore, you do something similar to this:

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

    public RequestRecoveryRedisCache(string regionName, IDictionary<string, string> properties, RedisCacheElement element, IRedisClientsManager clientManager)
        : base(regionName, properties, element, clientManager)
    {

    }

    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);
    }

    protected override void OnException(RedisCacheExceptionEventArgs e)
    {
        HttpContext.Current.Items[SkipNHibernateCacheKey] = true;
    }

    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, IRedisClientsManager clientManager)
    {
        return new RequestRecoveryRedisCache(regionName, properties, configElement, clientManager);
    }
}

And then use RequestRecoveryRedisCacheProvider in your app/web.config settings.

Changelog

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.

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Happy caching!