Question

Is there a universal way to instruct the DataContractJsonSerializer to use UTC for dates? Otherwise, I have to add .ToUniversalTime() to all of my date instances. Is this possible? The reason is that date values are defaulting DateTimeKind.Local and adding offsets to the JSON result. Making the dates universal does the trick, but can it be done at a global level? Thanks.

Answer 1

There’s no way to do that directly at the global level – primitive types (such as DateTime) can’t be “surrogated”. A possible workaround is to use some kind of reflection along with a surrogate to change the DateTime fields (or properties) in an object when it’s being serialized, as shown in the example below.

public class StackOverflow_6100587_751090
{
    public class MyType
    {
        public MyTypeWithDates d1;
        public MyTypeWithDates d2;
    }
    public class MyTypeWithDates
    {
        public DateTime Start;
        public DateTime End;
    }
    public class MySurrogate : IDataContractSurrogate
    {
        public object GetCustomDataToExport(Type clrType, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public object GetCustomDataToExport(MemberInfo memberInfo, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public Type GetDataContractType(Type type)
        {
            return type;
        }

        public object GetDeserializedObject(object obj, Type targetType)
        {
            return obj;
        }

        public void GetKnownCustomDataTypes(Collection<Type> customDataTypes)
        {
        }

        public object GetObjectToSerialize(object obj, Type targetType)
        {
            return ReplaceLocalDateWithUTC(obj);
        }

        public Type GetReferencedTypeOnImport(string typeName, string typeNamespace, object customData)
        {
            throw new NotImplementedException();
        }

        public CodeTypeDeclaration ProcessImportedType(CodeTypeDeclaration typeDeclaration, CodeCompileUnit compileUnit)
        {
            throw new NotImplementedException();
        }

        private object ReplaceLocalDateWithUTC(object obj)
        {
            if (obj == null) return null;
            Type objType = obj.GetType();
            foreach (var field in objType.GetFields())
            {
                if (field.FieldType == typeof(DateTime))
                {
                    DateTime fieldValue = (DateTime)field.GetValue(obj);
                    if (fieldValue.Kind != DateTimeKind.Utc)
                    {
                        field.SetValue(obj, fieldValue.ToUniversalTime());
                    }
                }
            }

            return obj;
        }
    }
    public static void Test()
    {
        MemoryStream ms = new MemoryStream();
        DataContractJsonSerializer dcjs = new DataContractJsonSerializer(typeof(MyType), null, int.MaxValue, true, new MySurrogate(), false);
        MyType t = new MyType
        {
            d1 = new MyTypeWithDates { Start = DateTime.Now, End = DateTime.Now.AddMinutes(1) },
            d2 = new MyTypeWithDates { Start = DateTime.Now.AddHours(1), End = DateTime.Now.AddHours(2) },
        };
        dcjs.WriteObject(ms, t);
        Console.WriteLine(Encoding.UTF8.GetString(ms.ToArray()));
    }
}