Protobuf-net serialization error = “The type cannot be changed once a serializer has been generated”

问题

The following scenario seems to cause the exception in Protobuf.net on deserialization. Have I done something wrong? Is there a way round this?

[ProtoContract]
[ProtoInclude(2, typeof(Ant))]
[ProtoInclude(3, typeof(Cat))]
public interface IBeast
{
    [ProtoMember(1)]
    string Name { get; set; }
}

[ProtoContract]
public class Ant : IBeast
{
    public string Name { get; set; }
}

[ProtoContract]
public class Cat : IBeast
{
    public string Name { get; set; }
}

[ProtoContract]
[ProtoInclude(1, typeof(AntRule1))]
[ProtoInclude(2, typeof(AntRule2))]
[ProtoInclude(3, typeof(CatRule1))]
[ProtoInclude(4, typeof(CatRule2))]
public interface IRule<T> where T : IBeast
{
    bool IsHappy(T beast);
}

[ProtoContract]
public class AntRule1 : IRule<Ant>
{
    public bool IsHappy(IAnt beast)
    {
        return true;
    }
}

[ProtoContract]
public class AntRule2 : IRule<Ant>
{
    public bool IsHappy(IAnt beast)
    {
        return true;
    }
}

[ProtoContract]
public class CatRule1 : IRule<Cat>
{
    public bool IsHappy(ICat beast)
    {
        return true;
    }
}

[ProtoContract]
public class CatRule2 : IRule<Cat>
{
    public bool IsHappy(ICat beast)
    {
        return true;
    }
}

public class TestSerialization
{
    public void Serialize()
    {
        var antRules = new List<IRule<Ant>>();
        antRules.Add(new AntRule1());
        antRules.Add(new AntRule2());

        var catRules = new List<IRule<Cat>>();
        catRules.Add(new CatRule1());
        catRules.Add(new CatRule2());

        using (var fs = File.Create(@"c:\temp\antRules.bin"))
        {
            ProtoBuf.Serializer.Serialize(fs, antRules);

            fs.Close();
        }

        using (var fs = File.OpenRead(@"c:\temp\antRules.bin"))
        {
            List<IRule<Ant>> list;
            list = ProtoBuf.Serializer.Deserialize<List<IRule<Ant>>>(fs);

            fs.Close();
        }

        using (var fs = File.Create(@"c:\temp\catRules.bin"))
        {
            ProtoBuf.Serializer.Serialize(fs, catRules);

            fs.Close();
        }

        using (var fs = File.OpenRead(@"c:\temp\catRules.bin"))
        {
            List<IRule<Cat>> list;
            list = ProtoBuf.Serializer.Deserialize<List<IRule<Cat>>>(fs);

            fs.Close();
        }
    }
}

回答1:

Ultimately I suspect the issue here is:

    [ProtoContract]
    [ProtoInclude(1, typeof(AntRule1))]
    [ProtoInclude(2, typeof(AntRule2))]
    [ProtoInclude(3, typeof(CatRule1))]
    [ProtoInclude(4, typeof(CatRule2))]
    public interface IRule<T> where T : IBeast

This says that for any T, IRule<T> has 4 children. This has the side effect of saying if you have more than one T, each of AndRule1...CatRule2 each have "n" parents, which isn't good. Let's instead assume that IRule<Ant> has 2 ant-rules, and so on... (after all, I doubt that CatRule1 is really an implementation of IRule<Ant>). Currently this can only be expressed via RuntimeTypeModel, since the attributes would always apply for all T:

[ProtoContract]
public interface IRule<T> where T : IBeast

and

// note these are unrelated networks, so we can use the same field-numbers
RuntimeTypeModel.Default[typeof(IRule<Ant>)]
    .AddSubType(1, typeof(AntRule1)).AddSubType(2, typeof(AntRule2));
RuntimeTypeModel.Default[typeof(IRule<Cat>)]
    .AddSubType(1, typeof(CatRule1)).AddSubType(2, typeof(CatRule2));

and then it works. Note the configuration only needs to be done once, usually at app-startup.

Thinking about it, I could probably just test at runtime, and in the case of generics simply ignore any that don't apply - by which I mean when evaluating IRule<Dog>, only consider the specific types if they implement IRule<Dog>. I'm still in two minds, though.

来源：https://stackoverflow.com/questions/7333233/protobuf-net-serialization-error-the-type-cannot-be-changed-once-a-serializer

标签

protobuf-net