Additional Providers

This section provides you with a brief introduction to some of the other providers that you can customize. Given what you have learned already about customizing the ProfileProvider, the MembershipProvider, and the RoleProvider, you should have no trouble using that knowledge to create your own custom providers for each of the items discussed in the rest of this section.

Introduction to the SessionState Provider

The session state provider is used to maintain session state for a web application. The session state is essentially a collection of name-value pairs that are associated with a session identifier. This session identifier is stored as a cookie (or embedded in the URL depending on session state configuration) on the client's machine. Each time a user requests a page, the session state for that user is accessible by means of the user's session identifier.

To create your own session state provider, you must override the SessionStateProviderBase class in the System.Web.SessionState namespace. The list of methods for that class is shown in Table 29.6.

Table 29.6. SessionStateStoreProviderBase Methods

Method	Description
CreateNewStoreData	Creates a new SessionStateStoreData instance for use with a web request
CreateUninitializedItem	Creates a new session state item to the data store
EndRequest	Invoked at the end of a request
GetItem	Obtains a session state item based on an ID and an HttpContext instance
GetItemExclusive	Gets an item and locks access to that item exclusively to the caller
InitializeRequest	Initializes a web request
ReleaseItemExclusive	Releases the exclusivity lock on a session state item obtained through GetItemExclusive
RemoveItem	Removes a state item name-value pair
ResetItemTimeout	Updates the expiration date of a session item
SetAndReleaseItemExclusive	Updates the session state item and clears the exclusive lock on the item
SetItemExpireCallback	Sets the delegate to be invoked when an item expires

Introduction to the SiteMap Provider

The SiteMap Provider is responsible for maintaining a site hierarchy. Essentially it is responsible for storing a tree structure, where each node in the tree has a description of a page as well as a link to that page. Site Map Providers make it possible to create "breadcrumb"-style controls that illustrate where a user is within a site hierarchy.

To create your own Site Map Provider, you need to create a class that inherits from System.Web.SiteMapProvider. The good thing about this particular provider is that not only does ASP.NET ship with an XML version, but the XML version is the default. Microsoft has provided an XmlSiteMapProvider that allows you to define your site map within an XML file.

However, if you are already storing your site map in a database such as SQL Server or Oracle in your own schema, you might want to create your own provider. Table 29.7 illustrates the methods of the SiteMapProvider class that you must override in order to implement your own custom Site Map Provider.

Table 29.7. SiteMapProvider Methods

Method	Description
FindSiteMapNode	Retrieves a SiteMapNode object based on a URL
FindSiteMapNodeFromKey	Finds a site map node based on the supplied key
GetChildNodes	Gets the child site map nodes of a given site map node
GetCurrentNodeAndHint-AncestorNodes	Retrieves the current site map node as well as a set number of ancestors (-1 for all)
GetCurrentNodeAndHint-NeighborhoodNodes	Retrieves the current site map node as well as neighborhood (under same parent) nodes
GetParentNode	Retrieves the parent node
GetParentNodeRelativeToCurrent-NodeAndHintDownFromParent	Optimized fetch for an ancestor node and the ancestor's descended nodes
GetParentNodeRelativeToNodeAnd-HintDownFromParent	Same as the preceding, but relative node is supplied rather than implied as "current"
HintAncestorNodes	Retrieves ancestor nodes of a given node
HintNeighborhoodNodes	Retrieves peer (same parent) nodes of a given node
Initialize	Initializes the SiteMapProvider
IsAccessibleToUser	Indicates whether the indicated site map node can be displayed to the user in the current context

The basic idea behind the site map provider is that the code is maintaining a tree structure with page-related information. You can come up with a fairly simple schema to manage this. The caveat here is that often many tree structures in relational databases perform slowly, so when implementing your own Site Map provider make sure to take advantage of the Hintxxxx methods and provide very fast (and cacheable) results.