Protobuf-net - list of objects with parent reference - list

Question

I have a simple class with reference to parent object. All objects are in one list (even parent objects). Is it possible to keep references references after deserialization?
In my code I have something like this:
[ProtoContract]
public class ProtoItem
{
[ProtoMember(1)]
public int Value { get; set; }
[ProtoMember(2, AsReference = true)]
public ProtoItem BaseItem { get; set; }
}
And main looks like that:
static void Main()
{
var itemParent = new ProtoItem { Value = 1 };
var item2 = new ProtoItem { Value = 2, BaseItem = itemParent };
var item3 = new ProtoItem { Value = 3, BaseItem = itemParent };
var parentListToWrite = new List<ProtoItem> {itemParent, item2, item3};
const string file = "protofile.txt";
try { File.Delete(file); }
catch { };
using (var fs = File.OpenWrite(file)) { Serializer.Serialize(fs,
parentListToWrite); }
List<ProtoItem> readList;
using (var fs = File.OpenRead(file)) { readList =
Serializer.Deserialize<List<ProtoItem>>(fs); }
if (readList[0] == readList[2].BaseItem)
{
//how to make it equal?
}
if (readList[0] == readList[1].BaseItem)
{
//how to make it equal?
}
}
Is it possible to deserialize that if conditions works?

Answer 1

The protobuf specification doesn't have the notion of object identity. protobuf-net does (as an optionally enabled feature), but it doesn't currently work for list items directly, although I suspect it probably should. Since it would break the format, though, it would need explicit enabling if I fixed this.
But the following code works today - note that what I have done here is to wrap the top-level list items in a wrapper that just encapsulates the ProtoItem, but in doing so enables reference-tracking. Not ideal, but: it works.
using ProtoBuf;
using System.Collections.Generic;
using System.IO;
[ProtoContract(AsReferenceDefault=true)]
public class ProtoItem
{
[ProtoMember(1)]
public int Value { get; set; }
[ProtoMember(2)]
public ProtoItem BaseItem { get; set; }
}
[ProtoContract]
public class Wrapper
{
[ProtoMember(1, DataFormat = DataFormat.Group)]
public ProtoItem Item { get;set; }
public static implicit operator ProtoItem(Wrapper value)
{
return value == null ? null : value.Item;
}
public static implicit operator Wrapper(ProtoItem value)
{
return value == null ? null : new Wrapper { Item = value };
}
}
static class Program
{
static void Main()
{
var itemParent = new ProtoItem { Value = 1 };
var item2 = new ProtoItem { Value = 2, BaseItem = itemParent };
var item3 = new ProtoItem { Value = 3, BaseItem = itemParent };
var parentListToWrite = new List<Wrapper> { itemParent, item2, item3 };
const string file = "protofile.txt";
try
{ File.Delete(file); }
catch
{ };
using (var fs = File.OpenWrite(file))
{
Serializer.Serialize(fs,
parentListToWrite);
}
List<Wrapper> readList;
using (var fs = File.OpenRead(file))
{
readList = Serializer.Deserialize<List<Wrapper>>(fs);
}
if (readList[0].Item == readList[2].Item.BaseItem)
{
//how to make it equal?
System.Console.WriteLine("eq");
}
if (readList[0].Item == readList[1].Item.BaseItem)
{
//how to make it equal?
System.Console.WriteLine("eq");
}
}
}