NHibernate.Cache.DynamicCacheBuster

Caching in NHibernate is awesome. But, what happens if your schema changes and your cache isn't cleared? For example, if you practice hot compatibility with your application (running two versions concurrently), you don't want your app to blow up if a column was added in the new version and the old cache isn't aware of it.

The typical solution is to bust the cache (use a new set of cache keys). You can do this by adding a version to the cache's region name. For example, with FluentNHibernate:

public class BlogMapping : ClassMap<Blog>
{
    public BlogMapping()
    {
        Cache.ReadWrite().Region("Blog.v2");
    }
}

This works well. We can have two versions of the cache running and there won't be any exceptions with different schemas.

What happens if you change your schema and you forget to update the cache version for busting? Uh-oh... 💥

This project fixes that problem by computing a hash of the schema so that you don't have to manually bust the cache.

Usage

1. Install the package:

   PM> Install-Package NHibernate.Cache.DynamicCacheBuster

2. Setup your NHibernate Configuration:

   var config = new Configuration();
   // Load all mappings...
   // Set your caching provider...
   // Enable second-level and query caches...

3. Append the computed versions (this is the magic!):

   new CacheBuster()
       .AppendVersionToCacheRegionNames(config);

4. Build the ISessionFactory and start using NHibernate:

   var sessionFactory = config.BuildSessionFactory();
   
   using (var session = sessionFactory.OpenSession())
   {
       // Use NHibernate as normal...
   }

Extras

• This project also computes hashes for collection caches.

• If you want to bust all of your model's caches (in addition to individual model changes) manually, you can use the cache.region_prefix setting. However, it has the same problem as cache region names for each model.

• This project is similar to how Shopify's IdentityCache does cache key generation for Ruby on Rails.

Changelog

2.1.0

• Add WithFormatRegionName to customize the formatting of the new region name.

2.0.0

• Remove WithLogging in favor of OnChange to include the old/new region names.

1.1.1

• Change default hash input functions to use type names instead of serializing the whole type.

1.1.0

• Add logging: buster.WithLogging(Logger)
• Add customization for RootClass hash input: buster.WithRootClassHashInput(GetRootClassHashInput)
• Add customization for Collection hash input: buster.WithCollectionHashInput(GetCollectionHashInput)
• Better hashing of RootClass that only looks at all properties (including collections and reference properties).
• .NET 4.0 and 4.5 packages.

1.0.0

• Initial release ✨.