How to customize error response in web api with .net core?

Question

I am using .net core 2.2 with web api. I have created one class i.e. as below :

public class NotificationRequestModel
{
    [Required]
    public string Dev         


        

Answer 1

As Chris analized, your issue is caused by Automatic HTTP 400 responses .

For the quick solution, you could supress this feature by

services.AddMvc()
        .ConfigureApiBehaviorOptions(options => {
            options.SuppressModelStateInvalidFilter = true;
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

For a efficient, you could follow suggestion from Chris, like below:

services.AddMvc()
        .ConfigureApiBehaviorOptions(options => {
            //options.SuppressModelStateInvalidFilter = true;
            options.InvalidModelStateResponseFactory = actionContext =>
            {
                var modelState = actionContext.ModelState.Values;
                return new BadRequestObjectResult(FormatOutput(modelState));
            };
        }).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

And, there is no need to define the code below any more in your action.

if (!ModelState.IsValid)
    {
        return BadRequest(FormatOutput(ModelState.Values));
    }