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Saturday, September 02, 2006

Session State Providers in Provider Model Pattern in ASP.NET Applications

Session state providers provide the interface between ASP.NET session state and session state data sources. The two most common reasons for writing a custom session state provider are:

  • You wish to store session state in a data source that is not supported by the session state providers included with the .NET Framework, such as an Oracle database.
  • You wish to store session state in a SQL Server database whose schema differs from that of the database used by System.Web.SessionState.SqlSessionStateStore.

Core ASP.NET session state services are provided by System.Web.SessionState.SessionStateModule, instances of which are referred to as session state modules. Session state modules encapsulate session state in instances of System.Web.SessionState.SessionStateStoreData, allocating one SessionStateStoreData per session (per user). The fundamental job of a session state provider is to serialize SessionStateDataStores to session state data sources and deserialize them on demand. SessionStateDataStore has three properties that must be serialized in order to hydrate class instances:

  • Items, which encapsulates a session's non-static objects
  • StaticObjects, which encapsulates a session's static objects
  • Timeout, which specifies the session's time-out (in minutes)

Items and StaticObjects can be serialized and deserialized easily enough by calling their Serialize and Deserialize methods. The Timeout property is a simple System.Int32 and is therefore also easily serialized and deserialized. Thus, if sssd is a reference to an instance of SessionStateStoreData, the core logic to write the contents of a session to a session state data source is often no more complicated than this:

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