Minimal APIs: How to Return Single Entity

[cornem]

I'm unable to find information about how to return a single entity using Minimal APIs and OData. All the samples I have found so far only include collections and functions/operations.

What I have tried:

app.MapGet("/api/customers/{id}", (id, ApplicationDbContext db) =>
{
     IQueryable<TEntity> query = db
         .Customers
         .AsNoTracking()
         .Where(e => e.Id == id);

    return SingleResult.Create(query);
})
    .AddODataQueryEndpointFilter()
    .WithODataModel(EdmModelBuilder.Model)
    .WithODataResult();

Doesn't work, results in an exception that says SingleResult wasn't found in the EDM model.

app.MapGet("/api/customers/{id}", (id, ApplicationDbContext db, ODataQueryOptions<TEntity> queryOptions) =>
{
     IQueryable<TEntity> query = db
         .Customers
         .AsNoTracking()
         .Where(e => e.Id == id);

    return queryOptions.ApplyTo(query).Cast<Customer>().FirstOrDefault();
})
    .WithODataModel(EdmModelBuilder.Model)
    .WithODataResult();

This results in an Entity Framework exception, about not being able to map SelectSome to Customer (makes sense).

What is the correct way to do this?

[TomasMoralesBarr]

Hi! The solution for returning a single entity with Minimal APIs is simpler than it might seem — you don't need SingleResult or manual ODataQueryOptions application for this use case.

Why your attempts failed

Attempt 1 (SingleResult.Create()):
SingleResult<T> is designed for traditional Controllers with [EnableQuery]. In the context of Minimal APIs, OData tries to resolve it as an EDM type, which it isn't, hence the "not found in the EDM model" error.

Attempt 2 (queryOptions.ApplyTo(...).Cast<Customer>().FirstOrDefault()):
ApplyTo() may return SelectSome<T> wrapper objects (used internally for $select/$expand projections) instead of plain Customer instances. Calling .Cast<Customer>() on that causes EF Core to fail since it can't translate SelectSome<Customer> to a SQL query.

---

✅ The correct approach

Simply return the entity directly and let .WithODataResult() + .WithODataModel() handle the OData serialization:

Option 1 – Simple single entity return (no query options)

IEdmModel model = EdmModelBuilder.Model;

app.MapGet("/api/customers/{id}", (int id, ApplicationDbContext db) =>
{
    return db.Customers
        .AsNoTracking()
        .FirstOrDefault(e => e.Id == id); // null → OData returns 404 automatically
})
    .WithODataResult()
    .WithODataModel(model);

Option 2 – With AddODataQueryEndpointFilter() (supports $select, $expand, etc.)

app.MapGet("/api/customers/{id}", (int id, ApplicationDbContext db) =>
{
    return db.Customers
        .AsNoTracking()
        .Where(e => e.Id == id); // return IQueryable<T>, the filter resolves it
})
    .AddODataQueryEndpointFilter()
    .WithODataResult()
    .WithODataModel(model);

Both will produce the expected OData response:

{
  "@odata.context": "http://localhost/$metadata#Customers/$entity",
  "Id": 1,
  "Name": "..."
}

---

Key takeaways

Method	Use case
.WithODataResult()	Serializes the response as OData JSON
.WithODataModel(model)	Provides the EDM model so OData generates the correct @odata.context (e.g. #Customers/$entity)
.AddODataQueryEndpointFilter()	Automatically applies query options ($select, $expand, etc.) over a returned IQueryable<T>
SingleResult<T>	Not for Minimal APIs — designed for Controllers with [EnableQuery] only

This pattern is covered by the existing E2E tests in the repository — see MinimalAPITodoEndpointsTest.cs for reference.

Hope this helps!