Question

I have a C# class with an object valued property. I am setting this property to an enum value , serialising to Json and then deserialising back to the object.

How can I make the object’s property value deserialise back to the enum?

That is, given:

public class Foo
{
   public object Value { get; set; }
}
public enum SmallNumbers { One, Two, Three }

How can I make this test pass?

   [Test]
   public void an_object_property_set_to_an_enum_can_be_serialised()
   {
      var settings = new JsonSerializerSettings
                        {
                           TypeNameHandling = TypeNameHandling.Auto
                        };

      var json = JsonConvert.SerializeObject(
         new Foo {Value = SmallNumbers.One},
         Formatting.None,
         settings);

      var foo = JsonConvert.DeserializeObject<Foo>(json, settings);

      Assert.That(foo.Value is SmallNumbers);
   }

Answer 1

It’s possible to write a converter for this special case but I won’t be helpful if you have many properties like ‘Value’ of type Object because there’s nothing to tell to which type to convert each Object. Check the code below & run the test on your machine.

using System;
using Newtonsoft.Json;
using NUnit.Framework;

class StackOverflowIssue7801000
{
    public enum SmallNumbers { One, Two, Three }

    public class Foo
    {
        public object Value { get; set; }
    }

    class ObjectToSmallNumbersConverter : JsonConverter
    {
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            // Not required for deserialization
            throw new NotImplementedException();
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            return (SmallNumbers)Convert.ToInt32(reader.Value);
        }

        public override bool CanConvert(Type objectType)
        {
            return (objectType == typeof(object));
        }
    }

    [Test]
    public void an_object_property_set_to_an_enum_can_be_serialised()
    {
        var settings = new JsonSerializerSettings {
            TypeNameHandling = TypeNameHandling.All
        };

        var json = JsonConvert.SerializeObject(new Foo { Value = SmallNumbers.Three }, Formatting.None, settings);
        settings.Converters.Add(new ObjectToSmallNumbersConverter());
        var foo = JsonConvert.DeserializeObject<Foo>(json, settings);
        Assert.That(foo.Value is SmallNumbers);
    }
}