Migrating Webapi Odata

ASP.NET Web API OData to ASP.NET Core OData Migration

Overview

Migrate OData services from ASP.NET Web API (Microsoft.AspNet.WebApi.OData or Microsoft.AspNet.OData) to ASP.NET Core OData (Microsoft.AspNetCore.OData). The core changes are registering OData via dependency injection with AddOData(), replacing convention-based routing with endpoint routing, and updating controllers to inherit from the ASP.NET Core ODataController base class. EDM model building remains similar but is wired differently.

Package Reference Changes

Old References (Remove)

<PackageReference Include="Microsoft.AspNet.WebApi.OData" Version="5.*" />
<PackageReference Include="Microsoft.AspNet.OData" Version="7.*" />

New Reference (Add)

<PackageReference Include="Microsoft.AspNetCore.OData" Version="{version-for-target-framework}" />

Workflow

Migration Progress:
- [ ] Step 1: Detect OData usage
- [ ] Step 2: Update project file references
- [ ] Step 3: Register OData in DI
- [ ] Step 4: Migrate controllers
- [ ] Step 5: Update EDM model configuration
- [ ] Step 6: Migrate routing
- [ ] Step 7: Build and verify

Step 1: Detect OData Usage

Scan the project for:

• using System.Web.OData; or using Microsoft.AspNet.OData; statements
• Controllers inheriting from ODataController or EntitySetController
• ODataConventionModelBuilder or ODataModelBuilder usage
• MapODataServiceRoute or MapODataRoute calls in WebApiConfig
• [EnableQuery] or [Queryable] attributes
• ODataQueryOptions<T> parameters

Step 2: Update Project File References

Remove old packages and add the new package reference (see "Package Reference Changes" above).

Step 3: Register OData in DI

Replace route-based OData registration with DI-based configuration in Program.cs or Startup.ConfigureServices:

// Old: in WebApiConfig.cs
var builder = new ODataConventionModelBuilder();
builder.EntitySet<Product>("Products");
config.MapODataServiceRoute("odata", "odata", builder.GetEdmModel());

// New: in Program.cs
builder.Services.AddControllers()
    .AddOData(options =>
    {
        options.Select().Filter().OrderBy().Expand().Count().SetMaxTop(100);
        options.AddRouteComponents("odata", GetEdmModel());
    });

Step 4: Migrate Controllers

• Change using directives from System.Web.OData or Microsoft.AspNet.OData to Microsoft.AspNetCore.OData.Routing.Controllers and Microsoft.AspNetCore.OData.Query
• Inherit from Microsoft.AspNetCore.OData.Routing.Controllers.ODataController instead of the legacy base class
• Replace EntitySetController<T, TKey> with ODataController — implement CRUD actions manually
• Keep [EnableQuery] attributes — they work in ASP.NET Core OData with the same semantics

Step 5: Update EDM Model Configuration

ODataConventionModelBuilder still exists in ASP.NET Core OData with a compatible API. Extract the model builder into a helper method:

static IEdmModel GetEdmModel()
{
    var builder = new ODataConventionModelBuilder();
    builder.EntitySet<Product>("Products");
    builder.EntitySet<Order>("Orders");
    return builder.GetEdmModel();
}

If using explicit ODataModelBuilder (non-convention), review property/navigation bindings — the API is mostly compatible but some extension methods have moved.

Step 6: Migrate Routing

| Old Pattern | New Pattern | Notes |

|------------|------------|-------|

| config.MapODataServiceRoute(name, prefix, model) | options.AddRouteComponents(prefix, model) | Registered inside AddOData |

| Convention routing with ODataRoute | Endpoint routing via attribute routes | Use [ODataAttributeRouting] or convention-based with AddRouteComponents |

| [ODataRoute("Products({key})")] | [HttpGet("Products({key})")] or convention routing | Explicit OData route attributes still supported |

| Batch endpoint ($batch) | options.AddRouteComponents(...).Services | Enable with routeOptions.EnableBatchRequests() |

For debugging route issues, enable the OData route debug endpoint:

app.UseODataRouteDebug();

This exposes /$odata to list all registered OData routes.

Step 7: Build and Verify

• Build the project:

   dotnet build

• Query the OData metadata endpoint to verify the EDM model:

   curl https://localhost:5001/odata/$metadata

• Test entity set queries with $select, $filter, and $expand to confirm query options work

Troubleshooting

404 on OData Endpoints

Verify the route prefix in AddRouteComponents matches the URL path. Check /$odata debug endpoint for registered routes.

$select / $filter Not Working

Ensure Select(), Filter(), and other query options are enabled in AddOData. ASP.NET Core OData disables all query options by default — they must be explicitly opted in.

EntitySetController Not Found

EntitySetController does not exist in ASP.NET Core OData. Inherit from ODataController and implement standard CRUD action methods (Get, Post, Put, Patch, Delete).

Serialization Differences

ASP.NET Core OData uses System.Text.Json by default. If entities have circular references or complex inheritance, configure serializer options or switch to Newtonsoft.Json via Microsoft.AspNetCore.OData.NewtonsoftJson.

Missing OData Route Attribute

If controller actions return 404, add [ODataAttributeRouting] to the controller or ensure convention routing matches the entity set name to the controller name (e.g., ProductsController for entity set Products).