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Interceptors (WCF Data Services)

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Important

WCF Data Services has been deprecated and will no longer be available for download from the Microsoft Download Center. WCF Data Services supported earlier versions of the Microsoft OData (V1-V3) protocol only and has not been under active development. OData V1-V3 has been superseded by OData V4, which is an industry standard published by OASIS and ratified by ISO. OData V4 is supported through the OData V4 compliant core libraries available at Microsoft.OData.Core. Support documentation is available at OData.Net, and the OData V4 service libraries are available at Microsoft.AspNetCore.OData.

RESTier is the successor to WCF Data Services. RESTier helps you bootstrap a standardized, queryable, HTTP-based REST interface in minutes. Like WCF Data Services before it, Restier provides simple and straightforward ways to shape queries and intercept submissions before and after they hit the database. And like Web API + OData, you still have the flexibility to add your own custom queries and actions with techniques you're already familiar with.

WCF Data Services enables an application to intercept request messages so that you can add custom logic to an operation. You can use this custom logic to validate data in incoming messages. You can also use it to further restrict the scope of a query request, such as to insert a custom authorization policy on a per request basis.

Interception is performed by specially attributed methods in the data service. These methods are called by WCF Data Services at the appropriate point in message processing. Interceptors are defined on a per-entity set basis, and interceptor methods cannot accept parameters from the request like service operations can. Query interceptor methods, which are called when processing an HTTP GET request, must return a lambda expression that determines whether an instance of the interceptor's entity set should be returned by the query results. This expression is used by the data service to further refine the requested operation. The following is an example definition of a query interceptor.

// Define a query interceptor for the Orders entity set.
[QueryInterceptor("Orders")]
public Expression<Func<Order, bool>> OnQueryOrders()

' Define a query interceptor for the Orders entity set.
<QueryInterceptor("Orders")> _
Public Function OnQueryOrders() As Expression(Of Func(Of Order, Boolean))

For more information, see How to: Intercept Data Service Messages.

Change interceptors, which are called when processing non-query operations, must return void (Nothing in Visual Basic). Change interceptor methods must accept the following two parameters:

  1. A parameter of a type that is compatible with the entity type of the entity set. When the data service invokes the change interceptor, the value of this parameter will reflect the entity information that is sent by the request.

  2. A parameter of type UpdateOperations. When the data service invokes the change interceptor, the value of this parameter will reflect the operation that the request is trying to perform.

The following is an example definition of a change interceptor.

// Define a change interceptor for the Products entity set.
[ChangeInterceptor("Products")]
public void OnChangeProducts(Product product, UpdateOperations operations)

' Define a change interceptor for the Products entity set.
<ChangeInterceptor("Products")> _
Public Sub OnChangeProducts(ByVal product As Product, _
                            ByVal operations As UpdateOperations)

For more information, see How to: Intercept Data Service Messages.

The following attributes are supported for interception.

[QueryInterceptor( EntitySetName )]
Methods with the QueryInterceptorAttribute attribute applied are called when an HTTP GET request is received for the targeted entity set resource. These methods must always return a lambda expression in the form of Expression<Func<T,bool>>.

[ChangeInterceptor( EntitySetName )]
Methods with the ChangeInterceptorAttribute attribute applied are called when an HTTP request other than HTTP GET request is received for the targeted entity set resource. These methods must always return void (Nothing in Visual Basic).

For more information, see How to: Intercept Data Service Messages.

See also