Daniel Dijkhuizen

I had the same issue and after debuging I found that the `ODataOutputFormatter` is returning false in the method `CanWriteResult` because it seems to be unable to determine the type...

Not directly. However, it's easily reproducible by using the [E2E EntitySetAggregation tests](test/Microsoft.AspNetCore.OData.E2E.Tests/EntitySetAggregation/EntitySetAggregationTests.cs) in this repository. The `EntitySetAggregationTests.AggregationOnEntitySetWorks(method: "average", expected: 100)` succeed normal where the `Get` -method in the [`EntitySetAggregationController`](test/Microsoft.AspNetCore.OData.E2E.Tests/EntitySetAggregation/EntitySetAggregationController.cs) is...

That's strange. I just forked this repository, cloned it to my machine, removed the `Skip` in the `Theory`-attribute on that test, and ran the test as-is. The database `EntitySetAggregationContext` is...

[OData.Issue.181.zip](https://github.com/OData/AspNetCoreOData/files/10328730/OData.Issue.181.zip) I've created and attached a small sample project based on the `EntitySetAggregationTests`. Hopefully this helps

The change ```c# [EnableQuery] [HttpGet("AsActionResult")] public ActionResult AsActionResult() { return _context.Customers; } ``` result still in a JSON result and not in an OData result when `$apply` is used. When...

> @cympatic did you perhaps forget to remove the `Ok(...)`? That is a very subtle detail but it actually makes a difference. Thanks! That was indeed the problem, I missed...

@julealgon is it fair to say that this issue is solved? Or at least explained well enough?