ASP.NET MVC How to convert ModelState errors to json

Question

How do you get a list of all ModelState error messages? I found this code to get all the keys: ( Returning a list of keys with ModelState errors)

var errorK         


        

Answer 1

The easiest way to do this is to just return a BadRequest with the ModelState itself:

For example on a PUT:

[HttpPut]
public async Task UpdateAsync(Update update)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    // perform the update

    return StatusCode(HttpStatusCode.NoContent);
}

If we use data annotations on e.g. a mobile number, like this, in the Update class:

public class Update {
    [StringLength(22, MinimumLength = 8)]
    [RegularExpression(@"^\d{8}$|^00\d{6,20}$|^\+\d{6,20}$")]
    public string MobileNumber { get; set; }
}

This will return the following on an invalid request:

{
  "Message": "The request is invalid.",
  "ModelState": {
    "update.MobileNumber": [
      "The field MobileNumber must match the regular expression '^\\d{8}$|^00\\d{6,20}$|^\\+\\d{6,20}$'.",
      "The field MobileNumber must be a string with a minimum length of 8 and a maximum length of 22."
    ]
  }
}