Handle ModelState Validation in ASP.NET Web API

Question

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?

Renaldorenard

Answer 1

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);
        }
    }
}

Treacle

The namespaces needed for this are System.Net.Http, System.Net System.Web.Http.Controllers, and System.Web.Http.Filters. – Theodolite

There is also a similar implementation at the official ASP.NET Web Api page: asp.net/web-api/overview/formats-and-model-binding/… – Friedland

Even if don't put [ValidationActionFilter] above web api, it still calls the code and give me bad request. – Cinchonidine

It's worth pointing out that the error response returned is controlled by the IncludeErrorDetailPolicy. By default the response to a remote request contains only a generic "An error has occurred" message, but setting this to IncludeErrorDetailPolicy.Always will include the detail (at the risk of exposing detail to your users) – Galsworthy

Is there a specific reason why you did not suggest using IAsyncActionFilter instead? – Aegaeon

The fact that this requires error details to be turned on for the whole site makes it useless, IMO. – Exaltation

Answer 2

Maybe not what you were looking for, but perhaps nice for someone to know:

If you are using .net Web Api 2 you could just do the following:

if (!ModelState.IsValid)
     return BadRequest();

Depending on the model errors, you get this result:

{
   Message: "The request is invalid."
   ModelState: {
       model.PropertyA: [
            "The PropertyA field is required."
       ],
       model.PropertyB: [
             "The PropertyB field is required."
       ]
   }
}

Manvell

Bare in mind when I asked this question Web API 1 was just released, it's probably moved on a lot since then :) – Renaldorenard

Be sure to mark the properties as optional, otherwise you'll get a non-helpful generic "An error has occurred." error message. – Soccer

Is there a way to change the Message? – Tiler

Answer 3

Like this, for example:

public HttpResponseMessage Post(Person person)
{
    if (ModelState.IsValid)
    {
        PersonDB.Add(person);
        return Request.CreateResponse(HttpStatusCode.Created, person);
    }
    else
    {
        // the code below should probably be refactored into a GetModelErrors
        // method on your BaseApiController or something like that

        var errors = new List<string>();
        foreach (var state in ModelState)
        {
            foreach (var error in state.Value.Errors)
            {
                errors.Add(error.ErrorMessage);
            }
        }
        return Request.CreateResponse(HttpStatusCode.Forbidden, errors);
    }
}

This will return a response like this (assuming JSON, but same basic principle for XML):

HTTP/1.1 400 Bad Request
Content-Type: application/json; charset=utf-8
(some headers removed here)

["A value is required.","The field First is required.","Some custom errorm essage."]

You can of course construct your error object/list any way you like, for example adding field names, field id's etc.

Even if it's a "one way" Ajax call like a POST of a new entity, you should still return something to the caller - something that indicates whether or not the request was successful. Imagine a site where your user will add some info about themselves via an AJAX POST request. What if the information they have tried to entered isn't valid - how will they know if their Save action was successful or not?

The best way to do this is using Good Old HTTP Status Codes like 200 OK and so on. That way your JavaScript can properly handle failures using the correct callbacks (error, success etc).

Here's a nice tutorial on a more advanced version of this method, using an ActionFilter and jQuery: http://asp.net/web-api/videos/getting-started/custom-validation

Bloated

That just returns my enquiry object, it doesn't say which properties are invalid though? So If I left CustomerAccountNumber empty, it should say the default validation message (CusomterAccountNumber field is required..) – Renaldorenard

I see, so is this the "correct" way of handling Model Validation then? Seems a bit messy to me.. – Renaldorenard

There are others ways to do it as well, like hooking up with jQuery validation. Here's a nice Microsoft example: asp.net/web-api/videos/getting-started/custom-validation – Bloated

This method and the method elected as the answer "should be" functionally identical, so this answer has the added value of showing you how you might do it yourself without an action filter. – Expensive

I had to change the line errors.Add(error.ErrorMessage); to errors.Add(error.Exception.Message); to get this working for me. – Apperceive

Answer 4

You can use attributes from the System.ComponentModel.DataAnnotations namespace to set validation rules. Refer Model Validation - By Mike Wasson for details.

Also refer video ASP.NET Web API, Part 5: Custom Validation - Jon Galloway

Other References

1. Take a Walk on the Client Side with WebAPI and WebForms
2. How ASP.NET Web API binds HTTP messages to domain models, and how to work with media formats in Web API.
3. Dominick Baier - Securing ASP.NET Web APIs
4. Hooking AngularJS validation to ASP.NET Web API Validation
5. Displaying ModelState Errors with AngularJS in ASP.NET MVC
6. How to render errors to client? AngularJS/WebApi ModelState
7. Dependency-Injected Validation in Web API

Bedfast

Answer 5

Or, if you are looking for simple collection of errors for your apps.. here is my implementation of this:

public override void OnActionExecuting(HttpActionContext actionContext)
    {
        var modelState = actionContext.ModelState;

        if (!modelState.IsValid) 
        {

            var errors = new List<string>();
            foreach (var state in modelState)
            {
                foreach (var error in state.Value.Errors)
                {
                    errors.Add(error.ErrorMessage);
                }
            }

            var response = new { errors = errors };

            actionContext.Response = actionContext.Request
                .CreateResponse(HttpStatusCode.BadRequest, response, JsonMediaTypeFormatter.DefaultMediaType);
        }
    }

Error Message Response will look like:

{
  "errors": [
    "Please enter a valid phone number (7+ more digits)",
    "Please enter a valid e-mail address"
  ]
}

Underweight

Answer 6

Add below code in startup.cs file

services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2).ConfigureApiBehaviorOptions(options =>
            {
                options.InvalidModelStateResponseFactory = (context) =>
                {
                    var errors = context.ModelState.Values.SelectMany(x => x.Errors.Select(p => new ErrorModel()
                   {
                       ErrorCode = ((int)HttpStatusCode.BadRequest).ToString(CultureInfo.CurrentCulture),
                        ErrorMessage = p.ErrorMessage,
                        ServerErrorMessage = string.Empty
                    })).ToList();
                    var result = new BaseResponse
                    {
                        Error = errors,
                        ResponseCode = (int)HttpStatusCode.BadRequest,
                        ResponseMessage = ResponseMessageConstants.VALIDATIONFAIL,

                    };
                    return new BadRequestObjectResult(result);
                };
           });

Clamworm

make sure the controller is marked with the attribute [ApiController] for handling as above – Dysarthria

Answer 7

C#

    public class ValidateModelAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext actionContext)
        {
            if (actionContext.ModelState.IsValid == false)
            {
                actionContext.Response = actionContext.Request.CreateErrorResponse(
                    HttpStatusCode.BadRequest, actionContext.ModelState);
            }
        }
    }

...

    [ValidateModel]
    public HttpResponseMessage Post([FromBody]AnyModel model)
    {

Javascript

$.ajax({
        type: "POST",
        url: "/api/xxxxx",
        async: 'false',
        contentType: "application/json; charset=utf-8",
        data: JSON.stringify(data),
        error: function (xhr, status, err) {
            if (xhr.status == 400) {
                DisplayModelStateErrors(xhr.responseJSON.ModelState);
            }
        },
....


function DisplayModelStateErrors(modelState) {
    var message = "";
    var propStrings = Object.keys(modelState);

    $.each(propStrings, function (i, propString) {
        var propErrors = modelState[propString];
        $.each(propErrors, function (j, propError) {
            message += propError;
        });
        message += "\n";
    });

    alert(message);
};

Fairly

Answer 8

Here you can check to show the model state error one by one

 public HttpResponseMessage CertificateUpload(employeeModel emp)
    {
        if (!ModelState.IsValid)
        {
            string errordetails = "";
            var errors = new List<string>();
            foreach (var state in ModelState)
            {
                foreach (var error in state.Value.Errors)
                {
                    string p = error.ErrorMessage;
                    errordetails = errordetails + error.ErrorMessage;

                }
            }
            Dictionary<string, object> dict = new Dictionary<string, object>();



            dict.Add("error", errordetails);
            return Request.CreateResponse(HttpStatusCode.BadRequest, dict);


        }
        else
        {
      //do something
        }
        }

}

Inspissate

Answer 9

I had an issue implementing the accepted solution pattern where my ModelStateFilter would always return false (and subsequently a 400) for actionContext.ModelState.IsValid for certain model objects:

public class ModelStateFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        if (!actionContext.ModelState.IsValid)
        {
            actionContext.Response = new HttpResponseMessage { StatusCode = HttpStatusCode.BadRequest};
        }
    }
}

I only accept JSON, so I implemented a custom model binder class:

public class AddressModelBinder : System.Web.Http.ModelBinding.IModelBinder
{
    public bool BindModel(HttpActionContext actionContext, System.Web.Http.ModelBinding.ModelBindingContext bindingContext)
    {
        var posted = actionContext.Request.Content.ReadAsStringAsync().Result;
        AddressDTO address = JsonConvert.DeserializeObject<AddressDTO>(posted);
        if (address != null)
        {
            // moar val here
            bindingContext.Model = address;
            return true;
        }
        return false;
    }
}

Which I register directly after my model via

config.BindParameter(typeof(AddressDTO), new AddressModelBinder());

Wilhelmstrasse

Answer 10

You can also throw exceptions as documented here: http://blogs.msdn.com/b/youssefm/archive/2012/06/28/error-handling-in-asp-net-webapi.aspx

Note, to do what that article suggests, remember to include System.Net.Http

Horn

Answer 11

Put this in the startup.cs file

 services.AddMvc().ConfigureApiBehaviorOptions(options =>
        {
            options.InvalidModelStateResponseFactory = (context) =>
            {
                var errors = context.ModelState.Values.SelectMany(x => x.Errors.Select(p =>p.ErrorMessage)).ToList();                    
                var result = new Response
                {
                    Succeeded = false,
                    ResponseMessage = string.Join(", ",errors)
                };
                return new BadRequestObjectResult(result);
            };
        });

Assignee