How to Implement OData v4 Service with XPO (.NET Core 3.1)

This example demonstrates how to create an ASP.NET Core 3.1 Web API project and provide a simple REST API using the XPO ORM for data access. For the .NET Framework-based example, refer to How to Implement OData v4 Service with XPO (.NET Framework).

Prerequisites

Visual Studio 2019 with the following workloads:
- ASP.NET and web development
- .NET Core cross-platform development
.NET Core SDK 3.1 or later

Steps To Implement

Step 1: Create Solution and Add Required Dependencies

Create a new ASP.NET Core Web Application project and select the API project template.
Install the following NuGet packages:
- DevExpress.Xpo
- Microsoft.AspNetCore.OData
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). These files contain helpers for demo data generation, LINQ and OData API extensions that will be used later.

Step 2: Define XPO and EDM Data Model

Create an XPO data model or add files from the CS\ODataService\Models folder in this example to your project. For more information on how to create your own data model, refer to the following articles: Create Persistent Class | Map to Existing Tables. Make sure that the CS\ODataService\Helpers\ConnectionHelper.cs file includes your custom persistent types.
Add the SingletonEdmModel.cs file to your project. The SingletonEdmModel.cs file demonstrates two ways to populate the EDM model with XPO classes. Also, in this file, we demonstrate how to add custom actions and functions (InitializeDatabase and TotalSalesByYear). For additional information, refer to the Convention model builder and Actions and Functions in OData v4 Using ASP.NET Web API 2.2 articles.

Step 3. Initialize Data Layer and Configure ASP.NET Core Middleware

Specify a connection string for your database in the CS\ODataService\appsettings.json file (Microsoft SQL Server LocalDB is used by default).

  "ConnectionStrings": {
    "MSSqlServer": "XpoProvider=MSSqlServer;data source=(LocalDB)\\MSSQLLocalDB;Integrated Security=true;MultipleActiveResultSets=true;initial catalog=ODataTest"
  }

Modify the ConfigureServices() method in the Startup.cs file to initialize the data layer and register XPO UnitOfWork and OData services in Dependency Injection.

  public void ConfigureServices(IServiceCollection services) {
  	services.AddOData();
  	services.AddODataQueryFilter();
      services.AddMvc(options => {
          options.EnableEndpointRouting = false;
          options.ModelValidatorProviders.Clear();
      });
  
      services.AddSingleton<IObjectModelValidator, CustomModelValidator>();
  
      services.AddXpoDefaultUnitOfWork(true, (DataLayerOptionsBuilder options) =>
          options.UseConnectionString(Configuration.GetConnectionString("MSSqlServer"))
          .UseAutoCreationOption(AutoCreateOption.DatabaseAndSchema) // debug only
          .UseEntityTypes(ConnectionHelper.GetPersistentTypes()));
  }

Modify the Configure() method in the Startup.cs file to add middleware for OData services and specify mapping for the service route. Note that we will pass the EDM model defined on the second step as a parameter (SingletonEdmModel.GetEdmModel()).

  public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {
      if (env.IsDevelopment())
      {
          app.UseDeveloperExceptionPage();
      }
  
      app.UseODataBatching();
  
      app.UseMvc(b =>
      {
          b.Count().Filter().OrderBy().Expand().Select().MaxTop(null);
          b.MapODataServiceRoute("odata", "odata", SingletonEdmModel.GetEdmModel(), new DefaultODataBatchHandler());
      });
  }

Step 4: Implement OData Controllers for CRUD and Actions/Functions

In the Controllers folder, add classes inherited from Microsoft.AspNet.OData.ODataController for each data model class created on the second step.
Implement the required methods in OData controllers (e.g., Get, Post, Put, Patch, Delete, etc.) as shown in this example (for instance, CS\ODataService\Controllers\CustomersController.cs).
Implement methods in an OData Controller for required OData Actions and Functions as shown in CS\ODataService\Controllers\ActionsController.cs.