Actions And Functions In OData V4 Using ASP.NET Web API

Action has a side effect on server, so that they are invoked by using HTTP POST requests. Action may have parameters and can have return type. The parameters and return type are described in the service metadata. The client sends the parameter values in in request body and server send the return value in response body.

In order to declare the action, we need to modify Web API configuration to add the action parameter to EDM (entity data model).

The EntityTypeConfiguration class has method called "Action" is used to add an action to the EDM (entity data model). The Parameter method is used to specify a typed parameter for defined action.
The above code is also specifying the namespace for the EDM. The namespace is required by URI and that includes with action name to create fully-qualified action name.



Definition of Action in OData controller

To enable "Rate" action, we need to add the following method to the EmployeeControler.
Here, I am using IIS expression to host service on development environment and I am using Telerik's Fiddler as a client application. Now, I am posting data using following URI in Fiddler.

URI - http://localhost:24367/Employee(1)/WebAPITest.Rate



The request body contains the parameter's value in form of JSON. Web API is automatically convert it in to ODataActionParameters object. This object is just dictionary type. This object can be used to retrieve value in controller.

When I am posting data using said URI, I am getting 404 –Not Found error. Here DOT (.) is present in URI; it will create issue with IIS and returns 404 error. We can resolve this issue by adding the following setting in web.config file.



Functions

There are two types of function supported by OData

1. Bound function
   
   The first step to add OData function to the controller is to modify the web API configuration. By using "function" method of EntityTypeConfiguration class, we can define the function and using "Returns" method we can define the return type of the function. The function can invoked by the client using GET request.
   
   1. ODataConventionModelBuilder builder = newODataConventionModelBuilder();
   2. builder.Namespace = "WebAPITest";
   3. builder.ContainerName = "DefaultContainer";
   4. builder.EntitySet<EmployeeRating>("EmployeeRating");
   5. builder.EntitySet<Employee>("Employee");
   7. builder.EntityType<Employee>().Collection
   8. .Function("GetHighestRating")
   9. .Returns<double>();
   Controller function definition as following-
   
   1. [HttpGet]
   2. publicIHttpActionResult GetHighestRating()
   3. {
   4. var rating = context.EmployeeRatings.Max(x => x.Rating);
   5. return Ok(rating);
   6. }
   Here URI pattern for the function is same Action I.e. namespace.functionname
   
   URL - http://localhost:24367/Employee/WebAPITest.GetHighestRating
   
   Output
   
   
   
   
   In the above example, function was bound to the collection. It is normally refer as Bound function.
   
   
2. Unbound function
   
   Unbound functions are normally not bound to any specific service and they are called as static operation on service.
   
   Following code change needs to be done in web API configuration-
   
   1. ODataConventionModelBuilder builder = newODataConventionModelBuilder();
   2. builder.Namespace = "WebAPITest";
   3. builder.ContainerName = "DefaultContainer";
   4. builder.EntitySet<EmployeeRating>("EmployeeRating");
   5. builder.EntitySet<Employee>("Employee");
   7. builder.Function("GetEmployeeRating")
   8. .Returns<double>()
   9. .Parameter<int>("EmployeeId");
   In the following function, I have passed employee id as parameter and function returns its rating. This function does not depends on the Employee type, so we can create this function in the separate controller. The [ODataRoute] attribute used to define the URI template for the function.
   
   1. [HttpGet]
   2. [ODataRoute("GetEmployeeRating(EmployeeId={employeeId})")]
   3. publicIHttpActionResult GetEmployeeRating(int employeeId)
   4. {
   5. var rating = context.Employees.Where(f => f.Id == employeeId).FirstOrDefault().EmployeeRating.Rating;
   6. return Ok(rating);
   7. }
   URL - http://localhost:24367/GetEmployeeRating(EmployeeId=1)
   
   Output
   
   
   

Summary

Web API 2 supports the Action and function with OData and it is very helpful to perform the operation which is not directly related to entity.