.NET WebAPI: throwing Bad Request instead of returning it

Question

I have a WebAPI controller and in circumstances I like to tell to the caller, that the content is malformed in form of a Bad Request response.

My operation method looks like this:

[HttpPost()]
public string Post([FromBody] ComplexType content) 
{
    // logic ...
}

I know that I can call this.BadRequest, but since my operation method has return type string, this helps me quite little.

How can I produce a Bad Request with the method shown above, without changing return type?

In that case your method has to throw an exception with the desired information. Additionally you have to add your own middleware that catches this exception and then returns the bad request response. But personally I like to use the ActionResult<> within the controller and handle these things in the concrete controller method. — Oliver
– Oliver, Commented Feb 15, 2022 at 14:06
Maybe this could be of help: stackoverflow.com/questions/53558342/… — Rahul Sharma
– Rahul Sharma, Commented Feb 15, 2022 at 14:14

Serge · Accepted Answer · 2022-02-15 20:14:46Z

2

Just change it to this

[HttpPost()]
public  ActionResult<string> Post([FromBody] ComplexType content) 
{
    // logic ...

    return "string";
    //or
    return Ok();
    //or       
    return BadRequest("string");
}

it will still returns string, but 400 error too

answered Feb 15, 2022 at 20:14

Serge

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haldo · Accepted Answer · 2022-02-15 14:40:41Z

2

You could decorate the Controller with [ApiController] attribute which will automatically add 400 BadRequest when ModelState is not valid.

The [ApiController] attribute makes model validation errors automatically trigger an HTTP 400 response. Consequently, the following code is unnecessary in an action method:
if (!ModelState.IsValid)
{
    return BadRequest(ModelState);
}

I've tested this for an Action which returns a string and the 400 error is sent successfully.

However, a better method (IMO) is to return an IActionResult (although you can still use [ApiController]). You then have more control over the response, and you could do something similar to the following:

[HttpPost()]
public IActionResult Post([FromBody] ComplexType content) 
{
    if (!ModelState.IsValid)
        return BadRequest();  // any custom message etc
    ...

    return Ok(yourString);
}

edited Feb 15, 2022 at 14:40

answered Feb 15, 2022 at 14:26

haldo

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1 Comment

user1470240 Over a year ago

Thanks for that idea, unfortunatelly I loose the return type here, what exactly I didn't wanted to. But the solution from Serge combines your approach with the implementation of ActionResult<T>

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