Inconsistent behaviour: Error response object in ASP.NET Core when manually return BadRequest

Question

I have a ASP.NET Core REST Api with both, static and dynamic validation.

When I not specify a required property, the middleware automatically generates a nice error message:

{
    "errors": {
        "status": [
            "Required property 'status' not found in JSON. Path '', line 37, position 1."
        ]
    },
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "|a6b5a076-4b400dadb53f75e7."
}

I also have some kind of dynamic validation where I manually populate the ModelState and return a BadRequest.

Simplified example:

ModelState.AddModelError("smh_data.materials.country_of_origin", "Field is required.");
return BadRequest(ModelState);

But in this case, the response looks like this:

{
    "smh_data.materials.country_of_origin": [
        "Field is required."
    ]
}

How can I get the same response object including traceId, type, title and status like above?

Answer 1

Instead of calling return BadRequest() , call return ValidationProblem() . This will create a ValidationProblemDetails object set to BadRequest , populate it with your ModelState errors, and return it.

Overloads of ValidationProblem() allow for further customisation of the returned response.