Nhibernate configuration cache

During an application's startup NHibernate can take significant time when configuring and validating it's mapping to a database. Caching the NHibernate configuration data can reduce initial startup time by storing the configuration to a file and avoiding the validation checks that run when a configuration is created from scratch.

SharpArch's NHibernateSession class now has a ConfigurationCache property that accepts an object reference that does the work of loading and saving the NHibernate configuration to a file. This new feature is based on an article by Oren Eini (aka Ayende Rahien) Building a Desktop To-Do Application with NHibernate, and a big thanks to Sandor Drieenhuizen who provided a lot of this code.

Cache Setup

To use the configuration cache simply set the NHibernateSession.ConfigurationCache property to a new instance of the NHibernateConfigurationFileCache class, before calling the NHibernateSession.Init method. For example:

private void InitializeNHibernateSession()
        {
            NHibernateSession.ConfigurationCache = new NHibernateConfigurationFileCache(
                new string[] { "Northwind.Domain" });
            NHibernateSession.Init(
                webSessionStorage,
                new string[] { Server.MapPath("~/bin/Northwind.Infrastructure.dll") },
                new AutoPersistenceModelGenerator().Generate(),
                Server.MapPath("~/NHibernate.config"));
        }
}

The constructor of the NHibernateConfigurationFileCache class takes a string array of file dependencies, typically this is the Domain.dll that contains the web application's domain model objects. The string array can contain just the assembly name (as above) or the file name (ex "Northwind.Domain.dll") or the full path to the file (ex "c:\inetput\wwwroot\bin\Northwind.Domain.dll").

Details

INHibernateConfigurationCache

Interface that defines two methods for loading and saving the configuration cache.

NHibernate.Cfg.Configuration LoadConfiguration(string configKey, string configPath, string[] mappingAssemblies) void SaveConfiguration(string configKey, NHibernate.Cfg.Configuration config)

These methods are used by the NHibernateSession.AddConfiguration method to load and save a configuration object to and from a cache file. This interface allows others to implement their own file caching mechanism if necessary.

NHibernateConfigurationCache

This class implements the interface and does the work of caching the configuration. Several methods are virtual so they can be overridden in a derived class, as may be necessary to store the cache file in a different location or to have different logic to invalidate the cache.

The constructor takes an string array of file dependencies which are used to test if the cached NHibernate configuration is current or not. If any of the dependent file's last modified time stamp is later than that of the cached configuration, then the cached file is discarded and a new configuration is created from scratch. This configuration is then serialized and saved to a file.

Note: NHibernate's XML config file and the mapping assemblies (ex "Northwind.Data.dll") are automatically included when testing if the cached configuration is current.

FileCache

The SharpArch.Domainproject now contains a FileCache class that can serialize and deserialize an object to a file in binary format. This class uses a generic type parameter to define the type being serialized and deserialized. This makes the FileCache class useful for any other object that you might want to serialize to a file.

NHibernateSession.ConfigurationCache property

This property holds a reference to an INHibernateConfigurationCache object, and if not null, will use the caching logic to load and save the NHibernate configuration. You must set the ConfigurationCache property before calling the NHibernateSession.Init method, and you cannot change the property reference after calling the Init method.

Configuration Serialization

To cache the configuration to a file, all objects contained within the NHibernate configuration must be serializable. All of the default data types included with NHibernate will serialize, but if you have any custom data types (i.e. classes that implement IUserType), they must also be marked with the [Serializable] attribute and, if necessary, implement ISerializable.