.NET Web API - Error Response with ModelState

Question

I'm building an API in C# with .NET Web API 2.2. I'm validating the request and returning an 'error' response via ModelState.

[ResponseType(typeof(IEnumerable<CustomerModel>))]
public IHttpActionResult Get([FromBody]List<CustomerSearchModel> row)
{
    if (ModelState.IsValid)
    {
        CustomerLookupModel model = new CustomerLookupModel(row);
        model.Init();
        model.Load();

        return Ok(model.Customers);
    }
    else
    {
        return BadRequest(ModelState);
    }
}

Here is a sample 'error' response.

{
    "message": "The request is invalid.",
    "modelState": {
        "row[0].Country": ["'Country' should not be empty."]
    }
}

In the 'error' response, I would like to change the word 'modelState' to 'error'. I thought I could do that by copying the 'ModelState' object and naming it 'error'... and include that with BadRequest.

return BadRequest(error);

That didn't work. I must be missing something simple.

Answer 1

Return anonymous object:

 public HttpResponseMessage GetModelStateErrors()
    {

        //return Request.CreateResponse(HttpStatusCode.OK, new Product());

        ModelState.AddModelError("EmployeeId", "Employee Id is required.");
        ModelState.AddModelError("EmployeeId", "Employee Id should be integer");
        ModelState.AddModelError("Address", "Address is required");
        ModelState.AddModelError("Email", "Email is required");
        ModelState.AddModelError("Email", "Invalid Email provided.");

        var error = new {
            message = "The request is invalid.",
            error = ModelState.Values.SelectMany(e=> e.Errors.Select(er=>er.ErrorMessage))
        };

        return Request.CreateResponse(HttpStatusCode.BadRequest, error);
    }

Fiddler output: