Is it possible to serialize a list of System.Object objects using protocol buffers

Question

I have a list of objects of various data types (DateTime, int, decimal, string).

List<object> myObjects = new List<object>();
myObjects.Add(3);
myObjects.Add(3.9m);
myObjects.Add(DateTime.Now);
myObjects.Add("HELLO");

I was able to serialize this list using protobuf-net, but deserialization always throws the exception: "Additional information: Type is not expected, and no contract can be inferred: System.Object".

using (var ms = new MemoryStream())
{
    Serializer.Serialize(ms, list2);
    var bytes = ms.ToArray();
    ms.Position = 0;
    var clone = Serializer.Deserialize(typeof(List<object>), ms); //Throws exception
}

I don't have any explicit contract, I suppose that is the problem? However, I do know what are the expected types of serialized objects, but how do I tell to protobuf-net?

Answer 1

Check these to see why this is a way to go:

1. The need for a parameterless constructor

2. why dynamic instead of object wouldn't have worked

3. why DynamicType=true wouldn't have worked

4. the need for an abstract base class and concrete implementations, by the creator of protobuf-net

5. why no serializer for object

Abstract base

    [ProtoContract]
    [ProtoInclude (1, typeof(ObjectWrapper<int>))]
    [ProtoInclude(2, typeof(ObjectWrapper<decimal>))]
    [ProtoInclude(3, typeof(ObjectWrapper<DateTime>))]
    [ProtoInclude(4, typeof(ObjectWrapper<string>))]
    abstract class ObjectWrapper {
        protected ObjectWrapper() {}
        abstract public object ObjectValue { get; set; }
    }

Implementation

    [ProtoContract()]
    class ObjectWrapper<T> : ObjectWrapper
    {
        public ObjectWrapper(): base() { }
        public ObjectWrapper(T t) { this.Value = t; }

        [ProtoIgnore()]
        public override object ObjectValue
        {
            get { return Value; }
            set { Value = (T)value; }
        }

        [ProtoMember(1)]
        public T Value { get; set; }
    }

Test

        var myObjects = new List<ObjectWrapper>();
        myObjects.Add(new ObjectWrapper<int>(3));
        myObjects.Add(new ObjectWrapper<decimal>(3.9m));
        myObjects.Add(new ObjectWrapper<DateTime> (DateTime.Now));
        myObjects.Add(new ObjectWrapper<string> ("HELLO"));
        var clone = Serializer.DeepClone(myObjects);