Serializing List using a surrogate with protobuf-net exception

Question

I'm using protobuf-net (version 2.0.0.621) and having a problem serializing List type where T is my own class (it does't matter what it contains) and a surrogate is set for T.

The surrogate is set like this:

ProtoBuf.Meta.RuntimeTypeModel.Default.Add(typeof(MyClass), false).SetSurrogate(typeof(MyClassSurrogate));

MyClass:

public class MyClass
{
    public int Number { get; set; }
}

[ProtoContract]
MyClassSurrogate
{
    [ProtoMember(1)]
    public int Number { get; set; }
}

Then I create a generic list of type MyClass instance, fill it with items and serialize it like this:

ProtoBuf.Serializer.Serialize(stream, list);

The problem occurs on deserialization, I keep getting "null" in the surrogate in the implicit operator conversion:

static public implicit operator MyClassSurrogate(MyClass myClass)

then 'myClass' is null.

If I remove the surrogate and decorate MyClass with the proto attributes, everything works fine.

Can you tell me what I'm doing wrong?

Thanks.

ignore comment if useless, just trying to help, but I never used protocol buffers. Anyway, question seems pretty basic, does this point you in the right direction? http://stackoverflow.com/questions/6498438/protobuf-net-cannot-serialize-type-data-how-can-i-define-type-data-with-protoc — bas, Feb 10 '13 at 09:32

Phillip Trelford · Accepted Answer · 2013-02-10T10:07:46.180

Adding a null check to the implicit operator conversion seems to fix the issue, i.e:

public static implicit operator MyClassSurrogate(MyClass myClass)
{
    return myClass != null ? new MyClassSurrogate { Number = myClass.Number } : null;
}

The implicit operator is initially called once with a null value on deserialization with the result appearing to be ignored.

Full implementation of MyClassSurrogate:

[ProtoContract]
public class MyClassSurrogate
{
    [ProtoMember(1)]
    public int Number { get; set; }

    public static implicit operator MyClassSurrogate(MyClass myClass)
    {
        return 
            myClass != null 
            ? new MyClassSurrogate { Number = myClass.Number } 
            : null;
    }

    public static implicit operator MyClass(MyClassSurrogate myClass)
    {
        return new MyClass { Number = myClass.Number };
    }
}

Full Serialization/Deserialization example:

var model = ProtoBuf.Meta.RuntimeTypeModel.Default;
model.Add(typeof(MyClassSurrogate), true);
model.Add(typeof(MyClass), false).SetSurrogate(typeof(MyClassSurrogate));
var stream = new System.IO.MemoryStream();
var list = new List<MyClass>();
for (int x = 0; x < 10; x++) list.Add(new MyClass { Number = x });            
ProtoBuf.Serializer.Serialize(stream, list);
stream.Seek(0, SeekOrigin.Begin);
var xs = ProtoBuf.Serializer.Deserialize<List<MyClass>>(stream);
foreach (var x in xs) Debug.WriteLine(x.Number);

Marc Gravell · Answer 2 · 2013-02-10T10:56:57.293

2

The value null is used pretty often, including during deserialization. You should be able to fix this simply by telling the conversion operator to translate null as null:

if(value == null) return null;

Thinking about it, I can probably safely add a "if both are reference types, translate null as null automatically".

edited Feb 10 '13 at 10:56

answered Feb 10 '13 at 10:01

Marc Gravell

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Serializing List using a surrogate with protobuf-net exception

2 Answers2