Question

I have this class

[Serializable]
public class myClass() : ISerializable
{
    public int a;
    public int b;
    public int c;

    public void GetObjectData(SerializationInfo info, 
                              StreamingContext context)
        {
        // Some code
        }

    public myClass(SerializationInfo info, 
                   StreamingContext context)
        {
        // Some code
        }
}

I have hundreds of these object in my database. I am now ready to publish a new version of my app where the class has morphed to

[Serializable]
public class myClass() : ISerializable
{
    public int a;
    public string b;
    public int c;
    public bool d;

    public void GetObjectData(SerializationInfo info, 
                              StreamingContext context)
        {
        // Some code
        }

    public myClass(SerializationInfo info, 
                   StreamingContext context)
        {
        // Some code
        }
}

How would one deserialize an object serialized based on the first version with the de-serialization constructor of the second.

Are there also strategies for future version proofing my second version of the class?

Answer 1

Without preparation on your part, you may need to resort to a hack: when your public myClass deserialization constructor gets the value of bool d, enclose the code in try/catch, and set d to its default value when you catch an exception.

In the future, add an int value "__ver" (or any other name that does not collide with arguments that you pass to info.AddValue), and set it to a constant that you maintain in your class to indicate compatible and incompatible changes in serialization:

public class myClass : ISerializable {
    private const int __ver = 4;
    public int a;
    public string b;
    public int c;
    public bool d;

    public void GetObjectData(SerializationInfo info, 
                          StreamingContext context) {
        info.AddValue("__ver", ver);
        info.AddValue("a", a);
        // and so on
    }

    public myClass(SerializationInfo info, 
               StreamingContext context) {
        switch(info.GetInt32("__ver")) {
            case 3: 
                // Deserialize prior version
            break;
            case 4: 
                // Deserialize current version
            break;
        }
    }
}