Question

Is it possible to deserialize part of a binary file?

Basically I have an object similar to below, which I serialize into a binary file.

public class MyObject
{
    public string Name { get; set; }

    public int Value { get; set; }

    public IList<MyOtherObject> { get; set; } // lots of data in here (order of kB-MB)
}

What I would like is to be able to deserialize only Name and Value by way of populating a ListView for file selection purposes and then deserialize the rest of the file when needed (i.e. the user chooses that file from the ListView).

As always, any help greatly appreciated and if any 3rd party libraries are suggested they would need to be able to be used freely in a commercial environment.

Answer 1

protobuf-net can do that, because it is not tied to the specific type; for example:

using ProtoBuf;
using System.Collections.Generic;
using System.IO;

[ProtoContract]
public class MyOtherObject { }
[ProtoContract]
public class MyObject
{
    [ProtoMember(1)]
    public string Name { get; set; }
    [ProtoMember(2)]
    public int Value { get; set; }
    [ProtoMember(3)]
    public IList<MyOtherObject> Items { get; set; }
}

[ProtoContract]
public class MyObjectLite
{
    [ProtoMember(1)]
    public string Name { get; set; }
    [ProtoMember(2)]
    public int Value { get; set; }
}

static class Program
{
    static void Main()
    {
        var obj = new MyObject
        {
            Name = "abc",
            Value = 123,
            Items = new List<MyOtherObject>
            {
                new MyOtherObject(),
                new MyOtherObject(),
                new MyOtherObject(),
                new MyOtherObject(),
            }
        };
        using (var file = File.Create("foo.bin"))
        {
            Serializer.Serialize(file, obj);
        }
        MyObjectLite lite;
        using (var file = File.OpenRead("foo.bin"))
        {
            lite= Serializer.Deserialize<MyObjectLite>(file);
        }
    }
}

But if you don’t want two different types, and/or you don’t want to have to add attributes – that can be done too:

using ProtoBuf.Meta;
using System.Collections.Generic;
using System.IO;

public class MyOtherObject { }
public class MyObject
{
    public string Name { get; set; }
    public int Value { get; set; }
    public IList<MyOtherObject> Items { get; set; }
}
static class Program
{
    static readonly RuntimeTypeModel fatModel, liteModel;
    static Program()
    {
        // configure models
        fatModel = TypeModel.Create();
        fatModel.Add(typeof(MyOtherObject), false);
        fatModel.Add(typeof(MyObject), false).Add("Name", "Value", "Items");
        liteModel = TypeModel.Create();
        liteModel.Add(typeof(MyOtherObject), false);
        liteModel.Add(typeof(MyObject), false).Add("Name", "Value");
    }
    static void Main()
    {
        var obj = new MyObject
        {
            Name = "abc",
            Value = 123,
            Items = new List<MyOtherObject>
            {
                new MyOtherObject(),
                new MyOtherObject(),
                new MyOtherObject(),
                new MyOtherObject(),
            }
        };
        using (var file = File.Create("foo.bin"))
        {
            fatModel.Serialize(file, obj);
        }
        MyObject lite;
        using (var file = File.OpenRead("foo.bin"))
        {
            lite = (MyObject)liteModel.Deserialize(
                file, null, typeof(MyObject));
        }
    }
}