c# - protobuf-net AddField 忽略 IgnoreListHandling

Question

我有这个数据结构声明:

[ProtoContract]
public class NotACollectionHolder
{
    public NotACollection some_objects;
}

[ProtoContract(IgnoreListHandling = true, ImplicitFields = ImplicitFields.AllPublic)]
public class NotACollection : IEnumerable<int>
{
    public int some_data;

    // something looks like a collection API
    public void Add(int a) { }
    public IEnumerator<int> GetEnumerator() { throw new NotImplementedException(); }
    IEnumerator IEnumerable.GetEnumerator() { throw new NotImplementedException(); }
}

我正在通过以下代码手动将字段注册到 MetaType:

MetaType meta = RuntimeTypeModel.Default.Add(typeof(NotACollectionHolder), false);
ValueMember member = meta.AddField(1, "some_objects", itemType: null, defaultType: null);
string proto = Serializer.GetProto<NotACollectionHolder>();

我将 NotACollection 标记为 IgnoreListHandling。我试图通过提供 itemType: null, defaultType: null 来强制 AddField 忽略 NotACollection 看起来像集合的事实。

不过，我的 member.ItemType 不为空，member.DefaultType 也不为空。并且 some_objects 成为生成的 proto 中的一个 repeated 字段:

message NotACollectionHolder {
    repeated int32 some_objects = 1;
}

我希望 proto 看起来像这样:

message NotACollection {
   optional int32 some_data = 1 [default = 0];
}
message NotACollectionHolder {
   optional NotACollection some_objects = 1;
}

我怎样才能做到这一点？我究竟做错了什么？我如何强制 protobuf-net 将此字段视为非集合字段？

提前致谢。

Answer 1

我认为这可能是 RuntimeTypeModel 的错误或限制应用程序接口(interface)。

确定是否为 ValueMember 的方法是一个集合是RuntimeTypeModel.ResolveListTypes() .当传入的 itemType 为 null 时，它会尝试推断集合项类型。仅使用静态属性为 NotACollectionHolder 构建合约时，例如:

var model = TypeModel.Create();
var schema = model.GetSchema(typeof(NotACollectionHolder));

然后 ProtoBuf.Meta.MetaType.ApplyDefaultBehaviour(bool isEnum, ProtoMemberAttribute normalizedAttribute)调用以创建初始化 ValueMember。它具有以下逻辑:

        // check for list types
        ResolveListTypes(model, effectiveType, ref itemType, ref defaultType);
        // but take it back if it is explicitly excluded
        if(itemType != null)
        { // looks like a list, but double check for IgnoreListHandling
            int idx = model.FindOrAddAuto(effectiveType, false, true, false);
            if(idx >= 0 && model[effectiveType].IgnoreListHandling)
            {
                itemType = null;
                defaultType = null;
            }
        }

注意到对 IgnoreListHandling 的显式检查了吗？这正确地阻止了 some_objects 被序列化为一个集合。

相反，如果以编程方式添加 ValueMember，如下所示:

var model = TypeModel.Create();
var meta = model.Add(typeof(NotACollectionHolder), false);
var member = meta.AddField(1, "some_objects", null, null);
var schema = model.GetSchema(typeof(NotACollectionHolder));

然后 MetaType.AddField(int fieldNumber, string memberName, Type itemType, Type defaultType, object defaultValue)被称为，它只是做:

        ResolveListTypes(model, miType, ref itemType, ref defaultType);

请注意没有检查IgnoreListHandling？这是你的问题的原因。

不幸的是，ValueType.itemType是只读的并且 MetaType[int fieldNumber]是只获取的，所以似乎没有一个简单的 API 可以调用来解决这个问题。你可以考虑 reporting an issue .

我能找到的唯一解决方法是为 NotACollectionHolder 类型引入一个代理项，如下所示:

[ProtoContract]
internal class NotACollectionHolderSurrogate
{
    [ProtoMember(1)]
    internal NotACollectionSurrogate some_objects;

    public static implicit operator NotACollectionHolder(NotACollectionHolderSurrogate input)
    {
        if (input == null)
            return null;
        return new NotACollectionHolder { some_objects = input.some_objects };
    }

    public static implicit operator NotACollectionHolderSurrogate(NotACollectionHolder input)
    {
        if (input == null)
            return null;
        return new NotACollectionHolderSurrogate { some_objects = input.some_objects };
    }
}

[ProtoContract]
internal class NotACollectionSurrogate
{
    [ProtoMember(1)]
    public int some_data;

    public static implicit operator NotACollection(NotACollectionSurrogate input)
    {
        if (input == null)
            return null;
        return new NotACollection { some_data = input.some_data };
    }

    public static implicit operator NotACollectionSurrogate(NotACollection input)
    {
        if (input == null)
            return null;
        return new NotACollectionSurrogate { some_data = input.some_data };
    }
}

然后做:

var model = TypeModel.Create();
model.Add(typeof(NotACollectionHolder), false).SetSurrogate(typeof(NotACollectionHolderSurrogate));

var schema = model.GetSchema(typeof(NotACollectionHolder));

生成的合约是按要求的:

message NotACollectionHolderSurrogate {
   optional NotACollectionSurrogate some_objects = 1;
}
message NotACollectionSurrogate {
   optional int32 some_data = 1 [default = 0];
}