protobuf-net AddField 忽略 IgnoreListHandling

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(); }
}

我正在手动将字段注册到MetaType通过以下代码：

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

I mark NotACollection with IgnoreListHandling。我尝试强迫AddField忽略这样一个事实NotACollection看起来像通过提供收集itemType: null, defaultType: null.

尽管如此，我有member.ItemType不为空，并且member.DefaultType也不为空。和some_objects成为了repeated生成的字段proto:

message NotACollectionHolder {
    repeated int32 some_objects = 1;
}

我预计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？如何强制 protobuf-net 将此字段视为非集合字段？

提前致谢。

我认为这可能是一个错误或限制RuntimeTypeModel https://www.codeproject.com/Articles/642677/Protobuf-net-the-unofficial-manual#without API.

判断是否存在的方法ValueMember https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/ValueMember.cs是一个集合是RuntimeTypeModel.ResolveListTypes() https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/RuntimeTypeModel.cs#L1851。当传入数据时，它会尝试推断集合项类型itemType一片空白。签订合同时NotACollectionHolder仅使用静态属性，例如通过执行以下操作：

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

Then ProtoBuf.Meta.MetaType.ApplyDefaultBehaviour(bool isEnum, ProtoMemberAttribute normalizedAttribute) https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/MetaType.cs#L1097被调用来创建一个初始化ValueMember。它有以下逻辑：

        // 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;
            }
        }

请注意显式检查IgnoreListHandling？这正确地防止了some_objects免于被序列化为集合。

相反，如果添加ValueMember以编程方式如下：

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));

Then MetaType.AddField(int fieldNumber, string memberName, Type itemType, Type defaultType, object defaultValue) https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/MetaType.cs#L1395被调用，它的作用很简单：

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

请注意，没有检查IgnoreListHandling？这就是你的问题的原因。

很遗憾，ValueType.itemType https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/ValueMember.cs#L36是只读的并且MetaType[int fieldNumber] https://github.com/mgravell/protobuf-net/blob/master/protobuf-net/Meta/MetaType.cs#L1546是 get-only，所以似乎没有一个简单的 API 可以调用来解决这个问题。你可能会考虑报告问题 https://github.com/mgravell/protobuf-net/issues.

我能找到的唯一解决方法是引入代理NotACollectionHolder像这样输入：

[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 };
    }
}

然后执行以下操作：

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

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

生成的合约按照要求：

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