Returning IActionResult and using an aggregate query produces non-OData JSON

[joshcomley]

Assemblies affected
Microsoft.AspNetCore.OData all of v8 and v9 as far as I can see.

Describe the bug
Run the ODataRoutingSample.

In the Customers controller, we return an IActionResult with an IQueryable:

public IActionResult Get()
{
    return Ok(GetCustomers());
}

If you call:

http://localhost:5000/v1/Customers

You will get an OData response:

{
  "@odata.context": "http://localhost:5001/v1/$metadata#Customers",
  "value": [
    {
      "Id": 1,
      "Name": "Jonier",
      "FavoriteColor": "Red",
      "Amount": 3,
      "HomeAddress": {
        "City": "Redmond",
        "Street": "156 AVE NE"
      },
      "FavoriteAddresses": [
        {
          "City": "Redmond",
          "Street": "256 AVE NE"
        },
        {
          "City": "Redd",
          "Street": "56 AVE NE"
        }
      ]
    },
    {
      "Id": 2,
      "Name": "Sam",
      "FavoriteColor": "Blue",
      "Amount": 6,
      "HomeAddress": {
        "@odata.type": "#ODataRoutingSample.Models.CnAddress",
        "City": "Bellevue",
        "Street": "Main St NE",
        "Postcode": "201100"
      },
      "FavoriteAddresses": [
        {
          "City": "Red4ond",
          "Street": "456 AVE NE"
        },
        {
          "City": "Re4d",
          "Street": "51 NE"
        }
      ]
    }
  ],
  "@odata.nextLink": "http://localhost:5001/v1/Customers?$skip=2"
}

But if you use an aggregate function:

http://localhost:5000/v1/Customers?$apply=groupby((FavoriteColor))

You will get a non-OData response:

[
  {
    "FavoriteColor": 0
  },
  {
    "FavoriteColor": 1
  }
]

However, if you return an IQueryable<T> directly and call the same aggregate query URL:

public IQueryable<Customer> Get()
{
    return GetCustomers().AsQueryable();
}

You get a proper OData response for the aggregate query:

{
  "@odata.context": "http://localhost:5001/v1/$metadata#Customers(FavoriteColor)",
  "value": [
    {
      "@odata.id": null,
      "FavoriteColor": "Red"
    },
    {
      "@odata.id": null,
      "FavoriteColor": "Green"
    }
  ],
  "@odata.nextLink": "http://localhost:5001/v1/Customers?$apply=groupby%28%28FavoriteColor%29%29&$skip=2"
}

Futher notes

If you return IQueryable only (not typed):

public IQueryable Get()
{
    return GetCustomers().AsQueryable();
}

You never get an OData response.

If you return IActionResult, do an aggregate query AND specify the DeclaredType in an OkObjectResult, you get the correct OData response back:

public IActionResult Get()
{
    return new OkObjectResult(GetCustomers())
    {
        DeclaredType = typeof(IQueryable<Customer>)
    };
}

Reproduce steps
Run the ODataRoutingSample and see the above steps.

Data Model
ODataRoutingSample - EdmModelBuilder.GetEdmModelV1()

EDM (CSDL) Model
NA

Request/Response
See above

Expected behavior
It should produce an OData response, even with an aggregate query returning an IActionResult.

Screenshots
NA

Additional context
NA

[xuzhg]

It's an known issue. I tried to fix it at: #1278, but it's still in the Draft.

We need to re-priority it to resume the fix.