By default, WCF Data Service will expose all data object collections provided by the data source in the format of OData entity sets. In addition to this, we can also add custom methods/operations on a given WCF Data Service. By using such custom operations, we can further extend our OData services so as to expose additional data in arbitrary formats, such as XML, JSON, and Binary.
In this recipe, we will demonstrate how to add custom operations to a WCF Data Service.
This sample case still uses the same ADO.NET Entity Framework based WCF Data Service like what we've discussed in the previous recipes. We will add some custom operations to it so as to expose additional data to client.
The source code for this recipe can be found in the \ch01\CustomOperationServiceSln\ directory.
1. Create a new ASP.NET Empty Web Application.
2. Create an ADO.NET Entity Framework based WCF Data Service through the Northwind sample database.
3. Add custom operations into the WCF Data Service class.
We will add two operations here, one for retrieving the current time on service server (return
DateTimevalue) and another for retrieving some test data entities of theCategoryentity type (see the following code snippet).public class NWDataService : DataService<CustomOperationService.NorthwindEntities> { ...... [WebGet] public DateTime GetServerTime() { return DateTime.Now; } [WebGet] public IQueryable<Category> GetDummyCategories() { var cates = new List<Category>(); cates.Add(new Category() { CategoryID = 1, CategoryName = "Category 1", Description = "Desc of Category 1" }); cates.Add(new Category() { CategoryID = 2, CategoryName = "Category 2", Description = "Desc of Category 2" }); cates.Add(new Category() { CategoryID = 3, CategoryName = "Category 3", Description = "Desc of Category 3" }); return cates.AsQueryable(); } }As the shown in the previous code, both operation functions need to be public and non-static member methods of the service class.
4. Enable the operation access rules in the service initialization code (see the following code snippet).
public static void InitializeService(DataServiceConfiguration config) { config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2; config.SetEntitySetAccessRule("*", EntitySetRights.All); config.SetServiceOperationAccessRule("*", ServiceOperationRights.All); }5. Select the
.svcfile to launch the service and directly invoke the custom operations (by typing the operation address) in the web browser.The following screenshot shows the web browser window after invoking the
GetServerTimeoperation:
The following is the output obtained by invoking the
GetDummyCategoriesoperation:
As shown in the previous sample code, we can add custom operations to WCF Data Service in the same way as we add service operations to a standard WCF REST service. Also, the WebGetAttribute attribute over each sample operation indicates that the operation can be accessed through the HTTP GET method (the expected method for operations that return data). We can also apply the WebInvokeAttribute attribute so as to make the operation support other HTTP methods.
Also, in order to allow clients to invoke custom operations, we need to grant the access rules in the InitializeService function just like we do for entity sets exposed in WCF Data Service.
For more information about access rules and permission configuration on WCF Data Service, see Chapter 7, Working with Security.