在 Protobuf-net 中，如何预先知道潜在类型的集合，如何传递包含不同类型对象的类型对象数组 [英] In Protobuf-net how can I pass an array of type object with objects of different types inside, knowing the set of potential types in advance

问题描述

我正在尝试将使用 XmlSerializer 的现有代码迁移到 protobuf-net，因为它提供了更高的性能，但是我在这个特定情况下遇到了问题.

I am trying to migrate existing code that uses XmlSerializer to protobuf-net due to the increased performance it offers, however I am having problems with this specific case.

我有一个对象[]，其中包含将要发送到远程主机(某种自定义的小型 rpc 工具)的参数.我知道这些参数可以来自的类型集，但我无法提前知道它们将按什么顺序发送.我有三个限制.第一个是我在 Compact Framework 中运行，所以我需要一些可以在那里工作的东西.其次，正如我提到的，性能是一个大问题(在序列化方面)，所以如果可能的话，我宁愿避免在那里使用大量反射.最重要的是我关心发送这些参数的顺序.使用 XmlSerializer 只需添加 XmlInclude 就很容易，但对于字段，据我所知在 Protobuf-net 中没有任何等效的东西.那么，有没有办法做到这一点?这是一个简化的例子.

I have an object[] that includes parameters that are going to be sent to a remote host (sort of a custom mini rpc facility). I know the set of types from which these parameters can be, but I cannot tell in advance in which order they are going to be sent. I have three constraints. The first is that I am running in Compact Framework, so I need something that works there. Second, as I mentioned performance is a big concern (on the serializing side) so I would rather avoid using a lot of reflection there if possible. And the most important is that I care about the order in which this parameters were sent. Using XmlSerializer it was easy just adding XmlInclude, but for fields there is nothing equivalent as far as I know in Protobuf-net. So, is there a way to do this? Here is a simplified example.

    [Serializable]
    [XmlInclude(typeof(MyType1)),
     XmlInclude(typeof(MyType2)),
     XmlInclude(typeof(MyType3))
    public class Message()
    {
         public object[] parameters;

         public Message(object[] parms)
         {
             parameters = parms; 
         }
    }

    Message m = new Message(new object[] {MyType1(), 33, "test", 
                new MyType3(), new MyType3()});
    MemoryStream ms = new MemoryStream();
    XmlSerializer xml = new XmlSerializer(typeof(Message));
    xml.Serialize(ms,xml);

这仅适用于 XmlSerializer，但如果我尝试将其转换为 protobuf-net，我将收到对象无默认编码"消息.

That will just work with XmlSerializer, but if I try to convert it to protobuf-net I will get a "No default encoding for Object" message.

我想出的最好的方法是使用泛型和 [ProtoInclude]，如下所示 示例.因为我可以在数组中拥有不同的对象类型，所以这并不完全正确.我为每个潜在类型添加了一个通用列表，并为 [ProtoIgnore] 添加了一个类型为 object[] 的属性来添加它们并获取它们.添加它们时我必须使用反射(以知道将每个项目放在哪个数组中)，这是不可取的，但我仍然无法保留顺序，因为我只是将每个列表中的所有项目一个一个地提取出来并将它们放入一个属性 get 上的 new object[] 数组.

The best I came up with is to use generics and [ProtoInclude] as seen in this example. Since I can have different object types within the array this doesn't quite make it. I added a generic List for each potential type and a property with [ProtoIgnore] with type object[] to add them and get them. I have to use reflection when adding them (to know in which array to put each item) which is not desirable and I still can't preserve the ordering as I just extract all the items on each list one by one and put them into a new object[] array on the property get.

我想知道有没有办法做到这一点?

I wonder if there is a way to accomplish this?

我尝试了 Marc 在下面的建议，但无法正常工作.我想我可能误解了一些东西.

I tried what Marc suggested below, but I couldn't get it to work. I think I may have misunderstood something.

使用您编写的代码.我想我应该使用 MessageParam Create 来生成 MessageParam 对象以添加到列表中.所以基本上我向 Message 添加了一个构造函数，如下所示:

Using the code you wrote. I thought I should use MessageParam Create to generate MessageParam objects to add to the list. So basically I added a constructor to Message like this:

public Message(object[] parms)
{
    foreach (object o in parms)
    {
        parameters.Add(MessageParam.Create(o));
    }
}

但是，如果我这样做，我会得到在序列化过程中发现意外类型；类型必须包含在 ProtoIncludeAttribute 中；发现 MessageParam`1 作为 MessageParam 传递"，因为我假设序列化程序需要非通用版本.我误解了你的建议吗?如果是这样，正确的做法是什么?

But, if i do that I will get "Unexpected type found during serialization; types must be included with ProtoIncludeAttribute; found MessageParam`1 passed as MessageParam" because I assume the serializer is expecting the non-generic version. Did I misunderstand your suggestion? If so, what is the right thing to do?

推荐答案

object 会有问题.我会尝试更像:

object is going to be problematic. I would try something more like:

[ProtoContract]
class Message
{
    private readonly List<MessageParam> parameters = new List<MessageParam>();
    [ProtoMember(1)]
    public List<MessageParam> Parameters { get { return parameters; } }
}
[ProtoContract]
[ProtoInclude(3, typeof(MessageParam<int>))]
[ProtoInclude(4, typeof(MessageParam<float>))]
[ProtoInclude(5, typeof(MessageParam<DateTime>))]
//...known types...
abstract class MessageParam {
    public abstract object UntypedValue { get; set; }
    public static MessageParam<T> Create<T>(T value) {
        return new MessageParam<T> { Value = value };
    }
    public static MessageParam CreateDynamic(object value)
    {
        Type type = value.GetType();
        switch (Type.GetTypeCode(value.GetType()))
        {
            // special cases
            case TypeCode.Int32: return Create((int)value);
            case TypeCode.Single: return Create((float)value);
            case TypeCode.DateTime: return Create((DateTime)value);
            // fallback in case we forget to add one, or it isn't a TypeCode
            default:
                MessageParam param = (MessageParam)Activator.CreateInstance(
                    typeof(MessageParam<>).MakeGenericType(type));
                param.UntypedValue = value;
                return param;
        }
    }
}
[ProtoContract]
sealed class MessageParam<T> : MessageParam
{
    [ProtoMember(1)]
    public T Value { get; set; }
    public override object UntypedValue
    {
        get { return Value; }
        set { Value = (T)value; }
    }
}

请注意，未发布的v2"代码提供了更多在运行时定义关系的能力，而不是通过属性(这在这里非常有限).

Note that the unreleased "v2" code offers much more ability to define the relationships at runtime rather than through attributes (which is quite limiting here).

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