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.

Answer 1

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