ProtoBuf-Net ProtoInclude Generic Type Subclass

Question

I'm having some problems with ProtoBuf-Net with a subclass of an object which inherits from a generic class.

My inheritance tree looks like this:

Node
    SomeNodeType
    SomeOtherType
    ResourceNode<T>
        ShipResource : ResourceNode<Ship>
        SomeResource : ResourceNode<SomeType>

I've been using ProtoInclude on the base Node type for all the normal types.

What would be the best way of achieving this hierarchy with protobuf-net? I've tried just including everything, but I get errors which seem to stem from protobuf trying to deserialise the object as one of it's parent objects.

For info, this scenario will work in the next release using just the attributes — Marc Gravell, Feb 29 '12 at 08:07

Marc Gravell · Accepted Answer · 2012-02-29T07:53:15.153

You're probably seeing:

A type can only participate in one inheritance hierarchy

at the moment, right?

The issue becomes clearer when you recall that ResourceNode<T> is not a closed type - but ResourceNode<Ship> and ResourceNode<SomeType> are. This means 2 things:

Firstly, Node needs to know separately about the two (ResourceNode<Ship> and ResourceNode<SomeType>), and secondly: we need to tell ResourceNode<Ship> about ShipResource only, and ResourceNode<SomeType> about SomeResource only.

The first is easy enough with the attribute approach:

[ProtoContract]
[ProtoInclude(1, typeof(SomeNodeType)), ProtoInclude(2, typeof(SomeOtherType))]
[ProtoInclude(3, typeof(ResourceNode<Ship>))]
[ProtoInclude(4, typeof(ResourceNode<SomeType>))]
public class Node { }

However, the second bit can't be cleanly expressed in any current release. We can't currently use:

[ProtoContract]
[ProtoInclude(1, typeof(ShipResource)), ProtoInclude(1, typeof(SomeResource))]
public class ResourceNode<T> : Node { }

since those attributes apply to both of ResourceNode<Ship> and ResourceNode<SomeType>, and represent illegal inheritance chains. The duplicated 1 in the above is intentional, as they are not in conflict, again because they are parallel branches.

What we can do, in v2, is configure this relationship explicitly:

RuntimeTypeModel.Default.Add(typeof(ResourceNode<Ship>), true)
     .AddSubType(1, typeof (ShipResource));
RuntimeTypeModel.Default.Add(typeof(ResourceNode<SomeType>), true)
     .AddSubType(1, typeof(SomeResource));

What I want to do is tweak the resolver such that it is able to detect this as a common-case, so that you can simply use the attributes:

[ProtoContract]
[ProtoInclude(1, typeof(ShipResource)), ProtoInclude(1, typeof(SomeResource))]
public class ResourceNode<T> : Node { }

I have added a "todo" item and failing test for this. However, interestingly while setting that up I also found a scenario where something isn't playing happily, so I'll need to fix that first

Excellent answer! Nice to hear it's going to be in a future release. The workaround works fine for now. (I added it to the static constructor for ResourceNode<>). Am I right in thinking that DynamicType etc are diverging quite far from the protobuf standard? — Simon Moles, Feb 23 '12 at 15:39
@Simie - watch out - the static ctor is per-T, and I is quite tricky to guess when it will fire. Mainly due to the tricky "when" I would avoid the .cctor for this. — Marc Gravell, Feb 23 '12 at 18:26
Yep, just found that out. I've moved it somewhere else. Thanks. — Simon Moles, Feb 23 '12 at 19:03

score 1 · Answer 2 · answered Sep 18 '13 at 07:23

I had the exact same problem, but rather than configuring all the types by hand, the method below seems to work for any type. Call it prior to serialization/deserialization.

private void PopulateTypes(Type t)
{
    foreach(object mt in RuntimeTypeModel.Default.GetTypes())
    {
        MetaType theType = mt as MetaType;
        if (null != theType)
        {
            if (theType.Type == t)
                return;
        }
    }

    Type objType = typeof (object);
    List<Type> inheritanceTree = new List<Type>();
    do
    {
        inheritanceTree.Insert(0, t);
        t = t.BaseType;
    } while (null != t && t != objType);

    if (!inheritanceTree.Any(gt => gt.IsGenericType))
        return;

    int n = 100;
    for (int i = 0; i < inheritanceTree.Count - 1; i++)
    {
        Type type = inheritanceTree[i];
        MetaType mt = RuntimeTypeModel.Default.Add(type, true);
        mt.AddSubType(n++, inheritanceTree[i + 1]);
    }
}

ProtoBuf-Net ProtoInclude Generic Type Subclass

2 Answers2

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