How to add a $count endpoint with attribute routing?

[sliekens]

Hi,

I'm experimenting with disabling the routing conventions and using only attribute routing.

One thing I've been unable to solve is that EntitySet routing convention also adds a /$count endpoint, and this is something I've not been able to reproduce using attribute routing.

I tried adding a new action to my controller with HttpGet("Documents/$count") where Documents is the name of my entity set.

[HttpGet("odata/Documents/$count")]
[EnableQuery]
public async Task<ActionResult<int>> CountDocuments() { }

However if I execute GET /odata/Documents/$count, I get a Bad Request response.

{
  "error": {
    "code": "",
    "message": "The query specified in the URI is not valid. The requested resource is not a collection. Query options $filter, $orderby, $count, $skip, and $top can be applied only on collections.",
    "details": [],
    "innererror": {
      "message": "The requested resource is not a collection. Query options $filter, $orderby, $count, $skip, and $top can be applied only on collections.",
      "type": "Microsoft.OData.ODataException",
      "stacktrace": "   at Microsoft.AspNetCore.OData.Query.EnableQueryAttribute.ValidateSelectExpandOnly(ODataQueryOptions queryOptions)\n   at Microsoft.AspNetCore.OData.Query.EnableQueryAttribute.ExecuteQuery(Object responseValue, IQueryable singleResultCollection, ControllerActionDescriptor actionDescriptor, HttpRequest request)\n   at Microsoft.AspNetCore.OData.Query.EnableQueryAttribute.OnActionExecuted(ActionExecutedContext actionExecutedContext, Object responseValue, IQueryable singleResultCollection, ControllerActionDescriptor actionDescriptor, HttpRequest request)"
    }
  }
}

2 candidate(s) found for the request path '/odata/Documents/$count'
Endpoint 'DocumentsController.CountDocuments (Api)' with route pattern 'odata/Documents/$count' is valid for the request path '/odata/Documents/$count'
Endpoint 'DocumentsController.GetDocument (Api)' with route pattern 'odata/Documents/{key}' is valid for the request path '/odata/Documents/$count'
Request matched endpoint 'DocumentsController.CountDocuments (Api)'

... (counting in progress) ...

List of registered output formatters, in the following order: ["Microsoft.AspNetCore.OData.Formatter.ODataOutputFormatter", "Microsoft.AspNetCore.OData.Formatter.ODataOutputFormatter", "Microsoft.AspNetCore.OData.Formatter.ODataOutputFormatter", "Microsoft.AspNetCore.Mvc.Formatters.HttpNoContentOutputFormatter", "Microsoft.AspNetCore.Mvc.Formatters.StringOutputFormatter", "Microsoft.AspNetCore.Mvc.Formatters.StreamOutputFormatter", "Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter"]
Attempting to select an output formatter based on Accept header '["application/json;odata.metadata=minimal;odata.streaming=true"]'.
Selected output formatter 'Microsoft.AspNetCore.OData.Formatter.ODataOutputFormatter' and content type 'application/json;odata.metadata=minimal;odata.streaming=true' to write the response.
Executing BadRequestObjectResult, writing value of type 'Microsoft.AspNetCore.Mvc.SerializableError'.
Executed action DocumentsController.CountDocuments (Api) in 494.4399ms
Executed endpoint 'DocumentsController.CountDocuments (Api)'
Request finished HTTP/2 GET https://localhost:5001/odata/Documents/$count?api-version=4.0 - - - 400 - application/json;+odata.metadata=minimal;+odata.streaming=true;+charset=utf-8 538.7744ms

So, I'm not sure what I need to do to make the $count work using only attribute routing?

Thanks for any help.

[xuzhg]

@sliekens What you added as '[HttpGet("odata/Documents/$count")]' is correct. But, the return type of your CountDocuments is not correct.

OData counts the number of 'Documents' based on the collection of 'Document', so returning an int can't work.

Please try to return collection of Document for your CountDocuments. Looking forward to your result.

[sliekens]

Thanks, I understand better now. I didn't realize I needed to return the entity set so OData can apply query options.

[mikepizzo]

As @xuzhg says, OData expects the path for /$count to return the collection of documents, so it can apply query options (i.e. $filter). So, you should be able to annotate a single GetDocuments controller method that returns all documents with both [HttpGet("odata/Documents")] and [HttpGet("odata/Documents/$count")]

[sliekens]

Aha, this worked. In hindsight, that makes the most sense, but couldn't figure it out! Thanks.