Asp.net webapi enum parameter with default value

Question

I have a controller

   [HttpGet]
    [RoutePrefix("api/products/{productId}")] 
    public HttpResponseMessage Products(int productId,TypeEnum ptype=TypeEnum.Clothes)
{
    if(!Enum.IsDefined(typeOf(TypeEnum),ptype))
      //throw bad request exception
    else
      //continue processing
}

Myenum is declared as

public TypeEnum
{
  Clothes,
  Toys,
  Electronics
}

Currently if,some garbage value is passed it is getting converted into default value. What I want to do is if i call the controller as api/products/1 then the ptype should be assigned default value i.e clothes. If I call the controller as api/products/1?pType=somegarbagevalue then the controller should throw bad request exception. How can I achieve this?

Answer 1

Defining all your enum parameters as strings and then parsing them everywhere means you have to do this on every single action and you will need to come up with a consistent approach such that all parsing errors conform.

This is a parameter binding issue and should not be dealt with in the controller layer, it should be taken care of in the pipeline. One way to do this is to create a custom filter and add it to your config.

public class ModelStateValidationAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        if (!actionContext.ModelState.IsValid)
        {
            actionContext.Response = <your standardised error response>
        }
    }
}

And in your global.asax.cs

...
GlobalConfiguration.Configure(WebApiConfig.Register);
...

public class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        ...
        config.Filters.Add(new ModelStateValidationAttribute());
        ...
    }
}

If you're having trouble with the model state, it's type is a ModelStateDictionary and you simply iterate over it and then it's Errors property contains all the model binding issues. e.g.

modelState = actionContext.ModelState;
modelState.ForEach(x =>
        {
            var state = x.Value;
            if (state.Errors.Any())
            {
                foreach (var error in state.Errors)
                {
                    <work your magic>
                }
            }
        });

Answer 2

You have to do with string and use TryParse() to convert string to Enum value.

public HttpResponseMessage Products(int productId,string ptype="Clothes")
{
    TypeEnum category = TypeEnum.Clothes;
    if(!Enum.TryParse(ptype, true, out category))
      //throw bad request exception if you want. but it is fine to pass-through as default Cloathes value.
    else
      //continue processing
}

It may look naive but the benefit of this approach is to allow ptype parameter to whatever string and to perform process without exception when ptype fails to bind the value.