C# – Handle ModelState Validation in ASP.NET Web API

asp.net-web-apic

I was wondering how I can achieve model validation with ASP.NET Web API. I have my model like so:

public class Enquiry
{
    [Key]
    public int EnquiryId { get; set; }
    [Required]
    public DateTime EnquiryDate { get; set; }
    [Required]
    public string CustomerAccountNumber { get; set; }
    [Required]
    public string ContactName { get; set; }
}

I then have a Post action in my API Controller:

public void Post(Enquiry enquiry)
{
    enquiry.EnquiryDate = DateTime.Now;
    context.DaybookEnquiries.Add(enquiry);
    context.SaveChanges();
}

How do I add if(ModelState.IsValid) and then handle the error message to pass down to the user?

Best Answer

For separation of concern, I would suggest you use action filter for model validation, so you don't need to care much how to do validation in your api controller:

using System.Net;
using System.Net.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;

namespace System.Web.Http.Filters
{
    public class ValidationActionFilter : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext actionContext)
        {
            var modelState = actionContext.ModelState;

            if (!modelState.IsValid)
                actionContext.Response = actionContext.Request
                     .CreateErrorResponse(HttpStatusCode.BadRequest, modelState);
        }
    }
}
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