ModelState Errormessage is Empty in Web API - asp.net

Question

Following is the Model class that I use for the application
public class APIVesselFilter
{
[Required(ErrorMessage = "Vessel is required")]
public Guid VesselID { get; set; }
public Guid? AnchorageID { get; set; }
}
Following is the Validation Filter that will check if the ModelState is Valid and if not valid I will send the error message.
public class ValidateModelAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext actionContext)
{
if (actionContext.ModelState.IsValid == false)
{
List<string> errorList = new List<string>();
foreach (var err in actionContext.ModelState.Values)
{
foreach (var er in err.Errors)
{
errorList.Add(er.ErrorMessage);
}
}
actionContext.Response = actionContext.Request.CreateResponse(APIResponse.SendResponse(RequestStatus.GetValidationFailedMessage(), actionContext.ModelState));
}
}
}
Here, Following is the response that I get using the above Model State. Over here the error message is not in a user understandable way and so I have added the ErrorMessage in Require attribute of Vessel and I loop through the errors in ModelState. But my error message is always empty (I checked this using a debugger). What am I missing here so that the error message will be bound directly to the ModelState?
{
"Status": {
"StatusCode": 620,
"StatusMessage": "Validation Failed"
},
"Data": {
"filter": {
"_errors": [
{
"<Exception>k__BackingField": {
"ClassName": "Newtonsoft.Json.JsonSerializationException",
"Message": "Required property 'VesselID' not found in JSON. Path '', line 1, position 56.",
"Data": null,
"InnerException": null,
"HelpURL": null,
"StackTraceString": " at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EndObject(Object newObject, JsonReader reader, JsonObjectContract contract, Int32 initialDepth, Dictionary`2 propertiesPresence)",
"RemoteStackTraceString": null,
"RemoteStackIndex": 0,
"ExceptionMethod": "8\nEndObject\nNewtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed\nNewtonsoft.Json.Serialization.JsonSerializerInternalReader\nVoid EndObject(System.Object, Newtonsoft.Json.JsonReader, Newtonsoft.Json.Serialization.JsonObjectContract, Int32, System.Collections.Generic.Dictionary`2[Newtonsoft.Json.Serialization.JsonProperty,Newtonsoft.Json.Serialization.JsonSerializerInternalReader+PropertyPresence])",
"HResult": -2146233088,
"Source": "Newtonsoft.Json",
"WatsonBuckets": null
},
"<ErrorMessage>k__BackingField": ""
}
],
"<Value>k__BackingField": null
}
}
}

Answer 1

Try decorating your model property with a DisplayAttribute:
public class APIVesselFilter
{
[Required]
[Display(Name="Vessel is required")]
public Guid VesselID { get; set; }
public Guid? AnchorageID { get; set; }
}
I know this is the way to customise your messages when using the Html.ValidationSummary and a quick test showed this comes up when inspecting the ModelState in an action.

Answer 2

using CreateErrorResponse instead of CreateResponse might solve your problem.
I faced a smiliar problem and was fixed with that.
In your case this will be
actionContext.Response = actionContext.Request.CreateErrorResponse(APIResponse.SendResponse(RequestStatus.GetValidationFailedMessage(), actionContext.ModelState));