Protobuf Inheritance and Generics

Question

I am attempting to use ProtoBuf net to serialize an object tree with the classes in the following format:

[ProtoContract]
class MySpecialCollectionList<T> : List<MySpecialCollection<T>>
{
    [ProtoMember(1)]
    public string Name { get; set; }
}

[ProtoContract]
class MySpecialCollection<T> : List<Special<T>>
{
    [ProtoMember(1)]
    public string Name { get; set; }
}

[ProtoContract]
class Special<T>
{
    [ProtoMember(1)]
    public string Name { get; set; }
    [ProtoMember(2)]
    public string Description { get; set; }

    [ProtoMember(3)]
    private readonly T _source; 
    T Source { get { return _source; } }

    private Special()
    {
    }

    public Special(T source) 
    { 
        _source = source; 
    }
}

interface IBeast
{
    string Name { get; set; }
}
[ProtoContract]
class Ant : IBeast
{
    [ProtoMember(1)]
    public string Name { get; set; }
}
[ProtoContract]
class Cat : IBeast
{
    [ProtoMember(1)]
    public string Name { get; set; }
}
[ProtoContract]
class Dog : IBeast
{
    [ProtoMember(1)]
    public string Name { get; set; }
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        MySpecialCollectionList<IBeast> collectionList = GetSpecialCollectionList();
        using (var fs = File.Create(@"c:\temp\protobuftest.bin"))
        {
            Serializer.Serialize(fs, collectionList);

            fs.Close();
        }
    }

    private MySpecialCollectionList<IBeast> GetSpecialCollectionList()
    {
        var ant = new Ant() { Name = "Mr Ant" };
        var cat = new Cat() { Name = "Mr Cat" };
        var dog = new Dog() { Name = "Mr Dog" };

        var Special = new Special<IBeast>(ant);

        var specialCollection1 = new MySpecialCollection<IBeast>() {
            {new Special<IBeast>(ant)},
            {new Special<IBeast>(cat)},
            {new Special<IBeast>(dog)}
        };
        specialCollection1.Name = "Special Collection1";


        var specialCollection2 = new MySpecialCollection<IBeast>() {
            {new Special<IBeast>(ant)},
            {new Special<IBeast>(dog)}
        };
        specialCollection2.Name = "Special Collection2";

        var specialCollectionList = new MySpecialCollectionList<IBeast>() {
            specialCollection1, specialCollection2 };

        specialCollectionList.Name = "Special Collection List";
        return specialCollectionList;
    }
}

Notice how the class I am serializing (MySpecialCollectionList<T>) is derived from a List<SomeOtherClass<T>>, not just List<T>.

I am struggling to work out where to put "ProtoInclude" attributes to get this to serialize all the items in the MySpecialCollectionList. Any help would be much appreciated.

Answer 1

Inheritance is not an issue here since even if A : B it is not true that Foo<A> : Foo<B>. Note that protobuf-net won't use a non-default constructor, although it is possible to skip the constructor, binding to the field directly (even readonly). While you may have 6 T, I can't see (from the code) that it would ever be in doubt which closed type you intend, and if the closed type is known you should be set.

If you have a Foo<SomeBaseClass> and a number of concrete types inherited from SomeBaseClass then the markers would o on SomeBaseClass.

However, if you have a concrete scenario I can use to reproduce your issue, I'll happily take a look.

---

Updated re edit:

There are a couple of key points drawn out in the example:

• in common with most binding APIs, XmlSerializer and IIRC DataContractSerializer, an item is either a list xor an item with values; if a collection (something implementing IList) has properties itself, they will not be serialized; encapsulation is preferred over inheritance here, i.e. something that has a Name and has a list (rather than has a Name and is a list)
• protobuf-net v1 does not support interface-based serialization; v2 does, but as with XmlSerializer and DataContractSerializer you need to explicitly tell it what things it needs to expect; quite nicely, though, we can move the [ProtoMember] onto the interface itself

Here's a fully working version in v2:

using System.Collections.Generic;
using ProtoBuf;
[ProtoContract]
class MySpecialCollectionList<T>
{
    [ProtoMember(1)]
    public string Name { get; set; }

    private readonly List<MySpecialCollection<T>> items = new List<MySpecialCollection<T>>();
    [ProtoMember(2)]
    public List<MySpecialCollection<T>> Items { get { return items; } }
}

[ProtoContract]
class MySpecialCollection<T>
{
    [ProtoMember(1)]
    public string Name { get; set; }

    private readonly List<Special<T>> items = new List<Special<T>>();
    [ProtoMember(2)]
    public List<Special<T>> Items { get { return items; } }
}

[ProtoContract]
class Special<T>
{
    [ProtoMember(1)]
    public string Name { get; set; }
    [ProtoMember(2)]
    public string Description { get; set; }

    [ProtoMember(3)]
    private readonly T _source;
    T Source { get { return _source; } }

    private Special()
    {
    }

    public Special(T source)
    {
        _source = source;
    }
}
[ProtoContract]
[ProtoInclude(2, typeof(Ant))]
[ProtoInclude(3, typeof(Cat))]
[ProtoInclude(4, typeof(Dog))]
interface IBeast
{
    [ProtoMember(1)]
    string Name { get; set; }
}
[ProtoContract]
class Ant : IBeast
{
    public string Name { get; set; }
}
[ProtoContract]
class Cat : IBeast
{
    public string Name { get; set; }
}
[ProtoContract]
class Dog : IBeast
{
    public string Name { get; set; }
}

public static class Form1
{

    private static void Main()
    {
        MySpecialCollectionList<IBeast> collectionList = GetSpecialCollectionList();
        var copy = Serializer.DeepClone(collectionList);
    }

    private static MySpecialCollectionList<IBeast> GetSpecialCollectionList()
    {
        var ant = new Ant() { Name = "Mr Ant" };
        var cat = new Cat() { Name = "Mr Cat" };
        var dog = new Dog() { Name = "Mr Dog" };

        var Special = new Special<IBeast>(ant);

        var specialCollection1 = new MySpecialCollection<IBeast>() {Items =
            {new Special<IBeast>(ant),
            new Special<IBeast>(cat),
            new Special<IBeast>(dog)}
        };
        specialCollection1.Name = "Special Collection1";


        var specialCollection2 = new MySpecialCollection<IBeast>()
        {
            Items =
            {new Special<IBeast>(ant),
            new Special<IBeast>(dog)}
        };
        specialCollection2.Name = "Special Collection2";

        var specialCollectionList = new MySpecialCollectionList<IBeast>()
        {
            Items ={
            specialCollection1, specialCollection2 }
        };

        specialCollectionList.Name = "Special Collection List";
        return specialCollectionList;
    }
}