Note: It is much easier to use the Web API Service with integrated authorization & CRUD operations based on ASP.NET Core OData 8.0 (OData v4) powered by EF Core and XPO ORM library instead. For more information, see A 1-Click Solution for CRUD Web API Services with Role-based Access Control via EF Core & XPO (FREE).

This example describes how to implement an OData v4 service with XPO and .NET Framework 4.5. This example is an ASP.NET MVC 5 Web API project and provides a simple REST API for data access. For the .NET Core-based example, refer to How to Implement OData v4 Service with XPO (.NET Core).

1. Create a new ASP.NET Web Application project and select the Web API project template (refer to the Create the Visual Studio Project section in this example for details.
2. Install the following nuget packages:
   • DevExpress.Xpo
   • Microsoft.AspNet.OData
3. Define your data model - implement persistent classes and initialize the data layer. If you are new to XPO, refer to the following articles to learn how to do this: Create Persistent Class, Map to Existing Tables.
4. Add files from the CS\OdataService\Helpers folder in this example to your project (Quick Tip: Add files to Visual Studio projects the easy way).
5. Modify the Application_Start() method declared in the Global.asax file: register the model body validator class and initialize the Data Access Layer.

protected void Application_Start() {
	GlobalConfiguration.Configuration.Services.Replace(typeof(IBodyModelValidator), new CustomBodyModelValidator());
	GlobalConfiguration.Configure(WebApiConfig.Register);
	XpoDefault.DataLayer = ConnectionHelper.CreateDataLayer(AutoCreateOption.SchemaAlreadyExists, true);
}

public class CustomBodyModelValidator : DefaultBodyModelValidator {
	readonly ConcurrentDictionary<Type, bool> persistentTypes = new ConcurrentDictionary<Type, bool>();
	public override bool ShouldValidateType(Type type) {
		return persistentTypes.GetOrAdd(type, t => !typeof(IXPSimpleObject).IsAssignableFrom(t));
	}
}

6. Modify the WebApiConfig.cs file: create an ODataModelBuilder instance and register an EntitySet for each persistent class (refer to the WebApiConfig.cs file in this repository to learn how to automatically register all persistent classes):

public static void Register(HttpConfiguration config) {
	config.Count().Filter().OrderBy().Expand().Select().MaxTop(null);
	ODataModelBuilder modelBuilder = CreateODataModelBuilder();

	ODataBatchHandler batchHandler =
		new DefaultODataBatchHandler(GlobalConfiguration.DefaultServer);

	config.MapODataServiceRoute(
		routeName: "ODataRoute",
		routePrefix: null,
		model: modelBuilder.GetEdmModel(),
		batchHandler: batchHandler);
}

static ODataModelBuilder CreateODataModelBuilder() { 

	// Include persistent classes to the EdmModel:
	ODataModelBuilder builder = new ODataConventionModelBuilder();
	var customers = builder.EntitySet<Customer>("Customers");
	customers.EntityType.HasKey(t => t.CustomerID);
	// ..

	// Include custom actions and functions into the EdmModel.
	builder.Function("TotalSalesByYear")
		.Returns<decimal>()
		.Parameter<int>("year");

	return builder;
}

7. Add OData controllers to the Controllers folder. An OData controller is a class inherited from the Microsoft.AspNet.OData.ODataController class. Each controller represents a separate data model class created on the third step.
8. Implement the required methods in controllers (e.g., Get, Post, Put, Patch, Delete, etc.). For reference, use existing controllers in this example. For example: CS\ODataService\Controllers\CustomersController.cs.

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