Validating Enums in Web api 2 object parameters

Question

Suppose you send a class-instance to controller and the class has a property of Enum type.

public class CoffeeController : ApiController
{
    [HttpPost]
    public async Task<IHttpActionResult> OrderAsync(Order request)
    {
        return Ok();
    }
}

public enum CoffeeType
{
    Latte,
    Mocha,
    Espresso
}

public class Order
{
    public CoffeeType Type { get; set; }
    public string Name { get; set; }
}

If there is an error in the name of enum member in request the application doesn't throw exception. It uses a default enum value instead:

{"name":"Dan", 'type':"ocha"}=>{"Name":"Dan", "Type":"Latte"}

This seems odd to me. Why such a behaviour is used?

Is there an elegant way to throw error?

Shashi Bhushan · Accepted Answer · 2017-02-17 15:38:34Z

1

It does this because Enums are based on an integer type , so they will always have a value (value types cannot be null) and will default to 0. Use following workaround

public enum CoffeeType
{
    Invalid = 0
    Latte = 1,
    Mocha = 2,
    Espresso = 3
}

answered Feb 17, 2017 at 15:38

Shashi Bhushan

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Comments

Brett Veenstra · Accepted Answer · 2017-02-17 15:38:44Z

1

Apply validation to your models. Create an ActionFilterAttribute and wire it into your pipeline or decorate your endpoint with it. Recommend you also consider FluentValidation as a great library to perform validation.

See ValidateModelStateFilter example in this article for a great example.

answered Feb 17, 2017 at 15:38

Brett Veenstra

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Comments

Sergey · Accepted Answer · 2017-02-17 16:27:04Z

As Brett writed you can use ModelState.IsValid and ModelState will have error. if you need just throw an error you can use custom media formatter for your type, like:

public class OrderJsonFormatter : BufferedMediaTypeFormatter
    {
        public OrderJsonFormatter()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/json"));
        }

        public override bool CanReadType(Type type)
        {
            var canRead = type == typeof(Order);
            return canRead;
        }

        public override bool CanWriteType(Type type)
        {
            return false;
        }

        public override object ReadFromStream(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)
        {
            return this.ReadFromStream(type, readStream, content, formatterLogger, CancellationToken.None);
        }

        public override object ReadFromStream(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger, CancellationToken cancellationToken)
        {
            using (var reader = new StreamReader(readStream))
            {
                using (var jsonReader = new JsonTextReader(reader))
                {
                    var jsonSerializer = new JsonSerializer();

                    if (type == typeof(Order))
                    {


                        try
                        {
                            var entity = jsonSerializer.Deserialize<Order>(jsonReader);
                            return entity;
                        }
                        catch (Exception ex)
                        {
                         //log error here
                            throw;
                        }
                    }

                    return null;
                }
            }
        }


    }

and register it :

 GlobalConfiguration.Configuration.Formatters.Insert(0, new OrderJsonFormatter());

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