How to configure OData in ASP.net Core?

 Integrating OData with ASP.net Core involves several steps, which are outlined below:

1. Install the required packages:

   • Microsoft.AspNetCore.OData
   • Microsoft.AspNetCore.Mvc.NewtonsoftJson (for Newtonsoft JSON serialization)

2. Add the OData service to the ASP.net Core services collection in the Startup.cs file:

   csharp
   using Microsoft.AspNet.OData.Extensions;
   ...
   public void ConfigureServices(IServiceCollection services)
   {
       ...
       services.AddOData();
       ...
   }

3. Configure the OData middleware in the Startup.cs file:

   csharp
   using Microsoft.AspNet.OData.Builder;
   using Microsoft.AspNet.OData.Extensions;
   using Microsoft.AspNet.OData.Formatter;
   using Microsoft.AspNetCore.Mvc;
   using Microsoft.OData.Edm;
   ...
   public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
   {
       ...
       app.UseRouting();
       app.UseEndpoints(endpoints =>
       {
           endpoints.MapControllers();
           endpoints.EnableDependencyInjection();
           endpoints.Select().Filter().Expand().OrderBy().MaxTop(1000);
           endpoints.MapODataRoute("odata", "api", GetEdmModel());
       });
       ...
   }
   private static IEdmModel GetEdmModel()
   {
       var builder = new ODataConventionModelBuilder();
       builder.EntitySet<Customer>("Customers");
       builder.EntitySet<Order>("Orders");
       return builder.GetEdmModel();
   }

4. Define OData controllers by inheriting from the ODataController class and defining actions to query data from the database:

   csharp
   using Microsoft.AspNet.OData;
   ...
   public class CustomersController : ODataController
   {
       private readonly ApplicationDbContext _context;
       public CustomersController(ApplicationDbContext context)
       {
           _context = context;
       }
       [HttpGet]
       [EnableQuery]
       public IActionResult Get()
       {
           return Ok(_context.Customers);
       }
       ...
   }

5. Configure the JSON serialization options in the Startup.cs file to use Newtonsoft JSON:

   csharp
   using Newtonsoft.Json.Serialization;
   ...
   public void ConfigureServices(IServiceCollection services)
   {
       ...
       services.AddControllers()
           .AddNewtonsoftJson(options =>
           {
               options.SerializerSettings.ContractResolver = new DefaultContractResolver();
           });
       ...
   }

With these steps, you should be able to properly integrate OData with ASP.net Core.