Question

I’m manually validating and adding the errors to my model as follows:

 var validationResult = model.Validate(new ValidationContext(model, null, null));

        foreach (var error in validationResult)
        {
            foreach (var memberName in error.MemberNames)
            {
                ModelState.AddModelError(memberName, error.ErrorMessage);
            }
        }

        if (!ModelState.IsValid)
        {

        }

If the model is not valid I want to return a JSON array containing the error messages. That’s tripping me up a little.

Answer 1

if (!ModelState.IsValid)
{
    return Json(
        ModelState
            .Where(x => x.Value.Errors.Count > 0)
            .Select(x => new 
            { 
                Key = x.Key, 
                Errors = x.Value.Errors.Select(e => e.ErrorMessage) 
            }
        ),
        JsonRequestBehavior.AllowGet
    );
}

or if you want only an array of the error messages:

if (!ModelState.IsValid)
{
    return Json(
        ModelState
            .Where(x => x.Value.Errors.Count > 0)
            .SelectMany(x => x.Value.Errors.Select(e => e.ErrorMessage))
            .Distinct(),
        JsonRequestBehavior.AllowGet
    );
}