Webapi post method with enum input parameter

Question

Why do I get the error in the screenshot below when attempting to call a Web API method that takes a enum as an input parameter? How do I resolve this?

It appears like the messageDestinationType is always null no matter what I do...

I would prefer to keep the input type as an enum. I am newish to using web apis and can't understand how this is so difficult when a WCF handles this scenario perfectly

[JsonConverter(typeof(StringEnumConverter))]    
public enum MessageDestinationType
{
    None = 0,
    [EnumMember(Value = "SMS")]
    SMS = 1,
    [EnumMember(Value = "Email")]
    Email = 2,
    PushNotification = 3,
    UXP = 4,
    IntermediaryApp = 5,
    YouthApp = 6
}



    [HttpPost, Route("ReadClientMessagesC")]
    public IHttpActionResult ReadClientMessagesC([FromBody]MessageDestinationType messageDestinationType)
    {
        var request = new ClientInboxRequest
        {
            Gcn = Gcn,
            ClientIpAddress = ClientIpAddress,
            CallingApplication = CallingApplication.Name,
            CallingApplicationVersion = CallingApplication.Version,
            CookieString = CookieString,
            HasPbUk = HasPbUk,
            HasIamIms = HasIamIms,
            HasPbZa = HasPbZa,
            HasSps = HasSps,
            HasWiUk = HasWiUk,
            HasWiZa = HasWiZa,
            LinkedGcns = LinkedGcns,
            RequestId = RequestId.ToString(),
            SsoProfiles = SsoProfiles.Select(x => x.Name).ToList()
        };

        MessageDestinationType messageDestination = (MessageDestinationType)messageDestinationType;

        return Ok(ClientMessageCenterHelper.ReadClientMessagesA(Gcn, messageDestination, request));
    }

Error message: { "Message": "The request is invalid.", "MessageDetail": "The parameters dictionary contains a null entry for parameter 'messageDestinationType' of non-nullable type 'API.Domain.ClientMessageCenter.MessageDestinationType' for method 'System.Web.Http.IHttpActionResult ReadClientMessagesC(API.Domain.ClientMessageCenter.MessageDestinationType)' in 'ID.ClientMessageCenter.Controllers.ClientMessageCenterController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter." }

Answer 1

You can send a string (string name of an enum) to the Web API Controller (even if it has a numeric value like the one in OP's example). ASP.NET framework already has provisions for this conversion to happen automatically - you just need to enable it.

In your Startup.cs ConfigureServices method, add your converter to the JsonSerializerOptions.Converters property.

services.AddControllers()
    .AddJsonOptions(opts =>
    {
        opts.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
        opts.JsonSerializerOptions.IgnoreNullValues = true;
    });

I would also suggest setting IgnoreNullValues as well to a setting of your preference to make it very explicit.

Credit: I solved my problem from this post (by regisdiogo) and shamelessly copied it here :-)

Answer 2

You should choose either a string or an integer in place of the enum for this.

Then parse this to your enum if you still need to use it.

Personally I would prefer an integer if I was consuming your RESTful API as you are effectively exposing a Type here. You could make these types available via a Get / GetAll method which keeps your API maintainable.

Answer 3

You have a few different options to solve this:

• If you can change the data that is being sent to ReadClientMessagesC, pass the data as an int (the Enum value) rather than the Enum description.
• If you can't change the incoming data, change the parameter type to string and use Enum.Parse in the method body or;
• Keep the method as written and use a custom model binder to convert the string to the MessageDestinationType.