NHibernate, by default, uses a first-level cache, or session-level cache. It means that, inside the same session, you can ask for the same object twice, and the database will be queried just once.

In addition, NHibernate also supports a second-level cache, or sessionfactory-level cache. It can cache object data among different sessions, drastically reducing the need for database queries.

Configuring ActiveRecord to use the second-level cache is quite easy:

Step 1: Configure

Within ActiveRecord configuration:

<config>
  <add key="hibernate.connection.driver_class" value="NHibernate.Driver.SqlClientDriver" />
  <add key="hibernate.dialect" value="NHibernate.Dialect.MsSql2000Dialect" />
  <add key="hibernate.connection.provider" value="NHibernate.Connection.DriverConnectionProvider" />
  <add key="hibernate.connection.connection_string" value="Data Source=.;Initial Catalog=myapp_db;Integrated Security=SSPI" />

  <add key="hibernate.cache.provider_class" value="NHibernate.Caches.SysCache.SysCacheProvider,NHibernate.Caches.SysCache" />
  <add key="relativeExpiration" value="300" />
</config>

Step 2: Copy necessary assemblies

Reference the assemblies that implements cache support. For the configuration above:

• NHibernate.Caches.SysCache.dll

Step 3: Enable cache for classes and relations

[ActiveRecord( Cache=CacheEnum.ReadOnly )]
public class Language : ActiveRecordBase 
{
  ...
  [HasMany(.... , Cache=CacheEnum.ReadOnly)]
  ...
  [HasAndBelongsToMany(.... , Cache=CacheEnum.ReadOnly)]
}

Notes

Make sure you understand how NHibernate caching works before enabling this feature. It can become particulary dangerous when your database is changed from outside NHibernate: either manually or by other applications.

Check NHibernate.Caches documentation for more information.

More information

For more information, check NHibernate documentation on enabling the second-level cache.

See also

• http://www.hibernate.org/hib_docs/nhibernate/1.2/reference/en/html/caches.html
• http://www.hibernate.org/hib_docs/nhibernate/1.2/reference/en/html/performance.html#performance-cache
• [Facility:ActiveRecord]