NHibernate with NCache

NHibernate has a first level or session level cache which is used by default. Each session contains its own session level cache which is not shared with other sessions. This cache is disposed whenever the session is closed. However, NHibernate allows to use second level, across session cache which spans across sessions’ life time and can be shared by multiple sessions.

NCache provides a second level or process level cache for NHibernate by implementing NHibernate's ICacheProvider and ICache interfaces. This enables NCache to be used as NHibernate second cache in existing NHibernate application without any code change. All that’s needed is to change NHibernate configuration file to plug-in NCache as cache provider and distributed caching can be used.

Second level cache can be configured by enabling the use of second level cache and configuring second level cache provider in NHibernate configurations.

Configuring NHibernate Application to use NCache as Second Level Cache

Create NHibernate region in Web.config

Add the <hibernate-configuration> in Web.config under the <configSections> tag:

<configSections>
  <section name="hibernate-configuration" type="NHibernate.Cfg.ConfigurationSectionHandler, NHibernate" />
  <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
</configSections>

Specify Configurations for NHibernate Region

• Place NCache’s NHibernate Provider assembly Alachisoft.NCache.Integrations.NHibernate.Cache.dll located at [InstallDir]/integration/nhibernate/assembly/ in the application's base directory.

• Configure NCache as NHibernate's second level cache provider by adding the cache.provider_class property under the specified region (<hibernate-configuration>).

• Enable the use of second level cache in application by setting the cache.use_second_level_cache property to true.

<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
   <session-factory>

     <property name="cache.provider_class">Alachisoft.NCache.Integrations.NHibernate.Cache.NCacheProvider, Alachisoft.NCache.Integrations.NHibernate.Cache</property>
     <property name="cache.use_second_level_cache">true</property>

   </session-factory>
 </hibernate-configuration>

Specify Application ID for NCache NHibernate Provider

NCache Provider for NHibernate identifies each application by an application ID. This ID is used to find the appropriate configuration for that application from NCache configuration file for NHibernate (NCacheNHibernate.xml). This application id must be specified in application's configuration file (Web.config):

  <appSettings>
    <add key="ncache.application_id" value="myapp" />
  </appSettings>

Configuring Cache Regions

NHibernate uses cache regions to store objects. NCache allows NHibernate cache regions to be configured with different properties. For this purpose, NCache has a configuration file named NCacheNHibernate.xml, which contains all regions’ configurations used by NHibernate Second Level Cache. This file can be placed at root directory of application or in [InstallDir]/config.

Sample NCacheNHibernate.xml

 <configuration>
   <application-config application-id="myapp" enable-cache-exception="true" default-region-name="default" key-case-sensitivity="false">
    <cache-regions>
        <region name="AbsoluteExpirationRegion" cache-name="demoClusteredCache"
        priority="Default" expiration-type="sliding" expiration-period="180" />

        <region name="default" cache-name="demoClusteredCache" priority="default"
        expiration-type="none" expiration-period="0" />
    </cache-regions>
  </application-config>
 </configuration>

Multiple application configurations can be specified in NCacheNHibernate.xml. Any NHibernate application will use one of the specified configurations based on the application-id specified in Web.config.

For more details on configurations and features supporting NHibernate like Configuring Cacheable Objects and Database Synchronization, refer to Using NCache as NHibernate Second Level Cache in Programmers' Guide.