使用MessagePack-Csharp nuget的多态性不适用于集合元素

Question

I'm not being able to deserialize a collection of elements where the instances have a Inheritance relationship between them.

Does anyone came across this issue?

So my use case is this: My model is similiar to this:

[DataContract]
    public class Item
    {
        [DataMember]
        public int Id { get; set; }

        [DataMember]
        public string Name { get; set; }

        [DataMember]
        public bool Valid { get; set; }


    }

    [DataContract]
    public class IntermediateItem : Item
    {
        [DataMember]
        public int Priority { get; set; }
    }

    [DataContract]
    public class ExtendedItem : IntermediateItem
    {
        [DataMember]
        public int Count { get; set; }

        [DataMember]
        public ItemsCollection Childs { get; set; }
    }

And Items Collection is something like this:

 [DataContract]
    public class ItemsCollection : Collection<Item>
    {
     }

The setup that I have made to ensure the proper deserialization is: Defining the CollectionFormatterBase:

 public class ItemCollectionFormatterBase : CollectionFormatterBase<Item, ItemsCollection>
    {
        protected override ItemsCollection Create(int count)
        {
            return new ItemsCollection();
        }

        protected override void Add(ItemsCollection collection, int index, Item value)
        {
            collection.Add(value);
        }
    }

The example that is not working, and not working I mean, the deserialized instances are all of base type, some how the inheritance relationship got lost in the serialization.

Example:

   MessagePack.Resolvers.CompositeResolver.RegisterAndSetAsDefault(new[] { new ItemCollectionFormatterBase() }, new[] { StandardResolver.Instance });


ExtendedItem instance = new ExtendedItem()
            {
                Id = 1,
                Name = "Extended Item",
                Priority = 121,
                Valid = true,
                Count = 10,
                Childs = new ItemsCollection(new List<Item>() { new Item() { Id = 1 }, new IntermediateItem() { Priority = 10 }, new ExtendedItem() { Count = 10 } })

            };

 byte[] bytes  = MessagePackSerializer.Serialize(instance);

          using (FileStream file = new FileStream(this.filePath.AbsolutePath, FileMode.Create))
            {
                await file.WriteAsync(bytes  , 0, payload.Length);
                await file.FlushAsync();
            }

  using (FileStream file = new FileStream(testsFolder + @"\ExtendedItem.msgPack-csharp.dat", FileMode.Open))
                {

                    file.Seek(0, SeekOrigin.Begin);
                    deserializedInstance =  MessagePackSerializer.Deserialize<ExtendedItem>(file);

                }

looking at the deserializedInstance Childs elements they all are from Item Type. Can you tell me what I'm doing wrong ? What is missing ?

A small update regarding Item definition:

 [DataContract]  
    [KnownType(typeof(IntermediateItem))]
    [KnownType(typeof(ExtendedItem))]
    public class Item
    {
        [DataMember]
        public int Id { get; set; }

        [DataMember]
        public string Name { get; set; }

        [DataMember]
        public bool Valid { get; set; }
    }

This also does not work. :(

Answer 1

Well looks like MessagePackSerializer static type as a static inner class called Typeless and that solve my problem:

With a instance of a ExtendedItem:

  ExtendedItem instance = new ExtendedItem()
            {
                Id = 1,
                Name = "Extended Item",
                Priority = 121,
                Valid = true,
                Count = 10,
                Childs = new ItemsCollection(new List<Item>() { new Item() { Id = 1 }, new IntermediateItem() { Priority = 10 }, new ExtendedItem() { Count = 10 } })

            };

I was able to serialize that and deserialize with success !

 byte[] bytes = MessagePackSerializer.Typeless.Serialize(instance);

                await fileManager.WriteAsync(bytes);

                ExtendedItem deserializedInstance = null;

                deserializedInstance = MessagePackSerializer.Typeless.Deserialize(bytes) as ExtendedItem;

despite the serialization and deserialization worked on .NET this sample did not work when deserializing in nodejs with msgpackjs package.