Question

I have two simple classes which I want to serialize with protobuf-net. Everything looks OK but when I deserialize the Body property is null. Any idea what I am doing wrong?

using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.Serialization;
using ProtoBuf;

namespace Protobuf_test
{
    public class Program
    {
        private static void Main(string[] args)
        {
            var innerObject = new Inner() { Id = Guid.NewGuid() };
            var outerObject = new Outer() { Body = innerObject };

            using (var stream = File.Create("serialized.bin"))
            {
                Serializer.Serialize(stream, outerObject);
            }
            using (var file = File.OpenRead("serialized.bin"))
            {
                var deserialized = Serializer.Deserialize<Outer>(file);
            }
        }
    }

    [DataContract]
    public class Inner
    {
        [DataMember]
        public Guid Id { get; set; }
    }

    [DataContract]
    public class Outer
    {
        [DataMember]
        public object Body { get; set; }
    }
}

Answer 1

Two issues:

1. protobuf-net requires a positive integer key per member; this can be provided via Order= on [DataMember]. Low numbers are better, so typically this means 1, 2, 3…

2. the protobuf specification is a schema-bound serializer; it wants to understand the data in advance; object does not work nicely.

but this would work:

[DataContract]
public class Inner
{
    [DataMember(Order=1)]
    public Guid Id { get; set; }
}

[DataContract]
public class Outer
{
    [DataMember(Order=1)]
    public Inner Body { get; set; }
}

There is some support for flexibly typed data (i.e. object), but note that it is protobuf-net specific (it will not play nicely re portability). I would encourage you to look at the typed approach first. But it can do that: I’d just prefer it if you didn’t ;p

If you cannot change the existing model, then the first thing I would advise would be: add a separate DTO model that looks a lot like your existing model, but marked for serialization, and work with that – and shim between the two models. If that isn’t an option, you’ll need to configure the system, to a: define keys for members, and b: tell it to use dynamic. For example:

var config = RuntimeTypeModel.Default;
config.Add(typeof(Inner),false).Add("Id");
config.Add(typeof(Outer), false).AddField(1, "Body").DynamicType = true;

(note: Serializer.* is basically a short-cut to RuntimeTypeModel.Default.*, so this configuration does talk to methods on Serializer.*)