DataContractJsonSerializer and Enums

Question

When I serialize a enum value using DataContractJsonSerializer, it serializes the numerical value of the enum, not the string name.

IE:

enum foo {    bar,    baz } 

Serializing a value of foo.bar returns "0", not "bar".

I'd prefer it the other way around, is there a way to override this?

Edit:

Because I didn't want to change the serializer, I used a simple workaround hack.

I exposed a property in the class to serialize that calls ToString on the value, ie:

// Old [DataMember] public EnumType Foo {     get { return _foo; }     set { _foo = value; } }  // New, I still kept the EnumType but I only serialize the string version  public EnumType Foo {     get { return _foo; }     set { _foo = value; } }  [DataMember] public string FooType {     get { return _foo.ToString(); }     private set {} } 

Answer 1

It looks like this is by design and this behavior cannot be changed:

Enumeration member values are treated as numbers in JSON, which is different from how they are treated in data contracts, where they are included as member names.

Here's an example using an alternative (and IMO better and more extensible) serializer which achieves what you are looking for:

using System; using Newtonsoft.Json;  class Program {     static void Main(string[] args)     {         var baz = Foo.Baz;         var serializer = new JsonSerializer();         serializer.Converters.Add(new JsonEnumTypeConverter());         serializer.Serialize(Console.Out, baz);         Console.WriteLine();     } }  enum Foo {     Bar,     Baz }  public class JsonEnumTypeConverter : JsonConverter {     public override bool CanConvert(Type objectType)     {         return objectType == typeof(Foo);     }     public override void WriteJson(JsonWriter writer, object value)     {         writer.WriteValue(((Foo)value).ToString());     }      public override object ReadJson(JsonReader reader, Type objectType)     {         return Enum.Parse(typeof(Foo), reader.Value.ToString());     } } 

Answer 2

I went crazy trying to find an elegant solution to this problem as it seems that everyone defaulted to Newtonsoft's serializer to workaround this issue. Though Newtonsoft provides more features, it does have some severe drawbacks. To enumerate a few: the need for parameterless constructors, crazy behaviour if you wish to serialize classes that implement IEnumerable, and it performs very badly when abstract types are used (as it does not make use of the KnownTypes attribute, and the workaround generates a verbose output that exposes your internal namespaces to callers).

On the other hand, there are little examples on how to customize the DataContractJsonSerializer when using it on an MVC4 WebApi solution.

It took me a while to find a solution that represents enums as strings and addresses the known DateTime formatting issues that comes with the DataContractJsonSerializer.

PART I - Put these extension methods in an extensions class ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#region JSon      /// <summary>Serializes an object to JSon.</summary>     /// <param name="obj">The object to serialize.</param>     /// <returns>Returns a byte array with the serialized object.</returns>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static byte[] SerializeJson(this object obj)     {         using (MemoryStream b = new MemoryStream())         {             SerializeJson(obj, b);             return b.ToArray();         }     }      /// <summary>Serializes an object to JSon.</summary>     /// <param name="obj">The object to serialize.</param>     /// <param name="stream">The stream to write to.</param>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static void SerializeJson(this object obj, Stream stream)     {         var settings = new DataContractJsonSerializerSettings();         settings.DateTimeFormat = new System.Runtime.Serialization.DateTimeFormat("yyyy-MM-dd'T'HH:mm:ssZ");         settings.DataContractSurrogate = new EnumToStringDataContractSurrogate();          var type = obj == null ? typeof(object) : obj.GetType();          var enumerationValue = obj as System.Collections.IEnumerable;          var fixedValue = enumerationValue != null                          ? type.IsGenericType && !type.GetGenericArguments()[0].IsInterface                             ? enumerationValue.ToArray(type.GetGenericArguments()[0])                             : enumerationValue.OfType<object>().ToArray()                          : obj;          if (enumerationValue != null && (!type.IsGenericType || (type.IsGenericType || type.GetGenericArguments()[0].IsInterface)))         {             var firstMember = (fixedValue as System.Collections.IEnumerable).OfType<object>().FirstOrDefault();             if (firstMember != null)                 fixedValue = enumerationValue.ToArray(firstMember.GetType());         }          var fixedType = obj == null                         ? type                         : fixedValue.GetType();          var jsonSer = new DataContractJsonSerializer(fixedType, settings);         jsonSer.WriteObject(stream, fixedValue);     }      /// <summary>     /// Deserializes an object.     /// </summary>     /// <typeparam name="T">The output type of the object.</typeparam>     /// <param name="data">The serialized contents.</param>     /// <returns>Returns the typed deserialized object.</returns>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("Microsoft.Naming", "CA1702:CompoundWordsShouldBeCasedCorrectly", MessageId = "JSon")]     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static T DeserializeJSon<T>(this byte[] data)     {         using (MemoryStream b = new MemoryStream(data))             return DeserializeJSon<T>(b);     }      /// <summary>Deserializes a JSon object.</summary>     /// <typeparam name="T">The output type of the object.</typeparam>     /// <param name="stream">The stream to read from.</param>     /// <returns>Returns the typed object.</returns>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("Microsoft.Naming", "CA1702:CompoundWordsShouldBeCasedCorrectly", MessageId = "JSon")]     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static T DeserializeJSon<T>(this Stream stream)     {         var settings = new DataContractJsonSerializerSettings();         settings.DateTimeFormat = new System.Runtime.Serialization.DateTimeFormat("yyyy-MM-dd'T'HH:mm:ssZ");         settings.DataContractSurrogate = new EnumToStringDataContractSurrogate();          var jsonSer = new DataContractJsonSerializer(typeof(T), settings);         return (T)jsonSer.ReadObject(stream);     }      /// <summary>Deserializes a JSon object.</summary>     /// <param name="data">The serialized contents.</param>     /// <param name="targetType">The target type.</param>     /// <returns>Returns the typed deserialized object.</returns>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("Microsoft.Naming", "CA1702:CompoundWordsShouldBeCasedCorrectly", MessageId = "JSon")]     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static object DeserializeJSon(this byte[] data, Type targetType)     {         using (MemoryStream b = new MemoryStream(data))         {             return DeserializeJSon(b, targetType);         }     }      /// <summary>Deserializes a JSon object.</summary>     /// <param name="data">The serialized contents.</param>     /// <param name="targetType">The target type.</param>     /// <returns>Returns the typed deserialized object.</returns>     /// <remarks>This implementation outputs dates in the correct format and enums as string.</remarks>     [SuppressMessage("Microsoft.Naming", "CA1702:CompoundWordsShouldBeCasedCorrectly", MessageId = "JSon")]     [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1650:ElementDocumentationMustBeSpelledCorrectly", Justification = "Reviewed.")]     public static object DeserializeJSon(this Stream data, Type targetType)     {         var settings = new DataContractJsonSerializerSettings();         settings.DateTimeFormat = new System.Runtime.Serialization.DateTimeFormat("yyyy-MM-dd'T'HH:mm:ssZ");         settings.DataContractSurrogate = new EnumToStringDataContractSurrogate();          var jsonSer = new DataContractJsonSerializer(targetType, settings);         return jsonSer.ReadObject(data);                 }      /// <summary>Enumerator contract surrogate.</summary>     internal class EnumToStringDataContractSurrogate : IDataContractSurrogate     {         Type IDataContractSurrogate.GetDataContractType(Type type)         {             return type == typeof(Enum) ? typeof(string) : type;         }          object IDataContractSurrogate.GetDeserializedObject(object obj, Type targetType)         {             if (targetType.IsEnum)             {                 return obj == null                        ? System.Enum.GetValues(targetType).OfType<int>().FirstOrDefault()                        : System.Enum.Parse(targetType, obj.ToString());             }             return obj;         }          object IDataContractSurrogate.GetObjectToSerialize(object obj, Type targetType)         {             if (obj is Enum)             {                 var pair = Enum.GetName(obj.GetType(), obj);                 return pair;             }              return obj;         }          object IDataContractSurrogate.GetCustomDataToExport(Type clrType, Type dataContractType)         {             throw new NotImplementedException();         }          object IDataContractSurrogate.GetCustomDataToExport(System.Reflection.MemberInfo memberInfo, Type dataContractType)         {             throw new NotImplementedException();         }          void IDataContractSurrogate.GetKnownCustomDataTypes(System.Collections.ObjectModel.Collection<Type> customDataTypes)         {             throw new NotImplementedException();         }          Type IDataContractSurrogate.GetReferencedTypeOnImport(string typeName, string typeNamespace, object customData)         {             throw new NotImplementedException();         }          System.CodeDom.CodeTypeDeclaration IDataContractSurrogate.ProcessImportedType(System.CodeDom.CodeTypeDeclaration typeDeclaration, System.CodeDom.CodeCompileUnit compileUnit)         {             throw new NotImplementedException();         }     }      #endregion       /// <summary>Creates an array from a non generic source.</summary>     /// <param name="source">The source.</param>     /// <param name="type">The target type of the array.</param>     /// <returns>Returns a typed array.</returns>     public static Array ToArray(this IEnumerable source, Type type)     {         var param = Expression.Parameter(typeof(IEnumerable), "source");         var cast = Expression.Call(typeof(Enumerable), "Cast", new[] { type }, param);         var toArray = Expression.Call(typeof(Enumerable), "ToArray", new[] { type }, cast);         var lambda = Expression.Lambda<Func<IEnumerable, Array>>(toArray, param).Compile();          return lambda(source);     } 

PART II - Create your own formatter by encapsulating the DataContractJsonSerializer ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/// <summary>Custom implementation of DataContract formatter.</summary> public class DataContractJsonFormatter : MediaTypeFormatter {      /// <summary>Creates a new instance.</summary>     public DataContractJsonFormatter()     {         SupportedMediaTypes.Add(new System.Net.Http.Headers.MediaTypeHeaderValue("application/json"));     }      /// <summary>Gets if the formatter the write a given type.</summary>     /// <param name="type">The type to handle.</param>     /// <returns>Returns if the formatter the write a given type.</returns>     public override bool CanWriteType(Type type)     {         return true;     }      /// <summary>Gets if the formatter the read a given type.</summary>     /// <param name="type">The type to handle.</param>     /// <returns>Returns if the formatter the read a given type.</returns>     public override bool CanReadType(Type type)     {         return true;     }      /// <summary>Deserializes an object.</summary>     /// <param name="type">The target type.</param>     /// <param name="readStream">The stream to read from.</param>     /// <param name="content">The http content.</param>     /// <param name="formatterLogger">A logger.</param>     /// <returns>Returns the deserialized object.</returns>     public override Task<object> ReadFromStreamAsync(Type type, Stream readStream, System.Net.Http.HttpContent content, IFormatterLogger formatterLogger)     {         var task = Task<object>.Factory.StartNew(() =>         {             return readStream.DeserializeJSon(type);         });          return task;     }      /// <summary>Serializes an object.</summary>     /// <param name="type">The target type.</param>     /// <param name="value">The object to serialize.</param>     /// <param name="writeStream">The stream to write to.</param>     /// <param name="content">The http content.</param>     /// <param name="transportContext">The context.</param>     /// <returns>Returns the deserialized object.</returns>     public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, System.Net.Http.HttpContent content, System.Net.TransportContext transportContext)     {         var task = Task.Factory.StartNew(() =>         {             value.SerializeJson(writeStream);         });          return task;     } } 

PART III - Edit your Global.asax file and consume your new JSon formatter ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    /// <summary>Event handlers of when the application starts.</summary>     [SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic")]     protected void Application_Start()     {        //Register my custom DataContract JSon serializer         GlobalConfiguration.Configuration.Formatters.Insert(0, new DataContractJsonFormatter());          //Register areas         AreaRegistration.RegisterAllAreas();          WebApiConfig.Register(GlobalConfiguration.Configuration);         FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);         RouteConfig.RegisterRoutes(RouteTable.Routes);        // BundleConfig.RegisterBundles(BundleTable.Bundles);          //JSON serialization config         var json = GlobalConfiguration.Configuration.Formatters.JsonFormatter;         json.UseDataContractJsonSerializer = false;     }