Question

Is there any way to save an entire class definition for a C# object to a file / data store?

I use the [Serializable] tag and ISerializable interface to do this already, but both of these rely on the object definition being in the assembly at run time.

What I’m looking for is a solution to the following scenario:

1) User creates object MyClass in my software and saves it

For the purpose of this example, MyClass is a stand-alone object that doesn’t rely on any other class in the system:

i.e. this could be the entire definition:

public class MyClass
{
    public int MyProperty { get; set; }
    public void DoSomething() { /* do something, like Console.Write(""); */ }
}

2) We release a patch that removes MyClass from the system

3) User loads the saved MyClass from step 1 and calls DoSomething() on it – and has the function work exactly the same as it did before the patch removed the class from the system

---

Is there any way this can be done without reflection / emit trickery?

Answer 1

No, this won’t work without emitting the type definition. What you are trying to do is actually save off the code (otherwise, how would DoSomething work?) – which is what the compiler does for you. Plain serialization will never work for you here.

So, if you need to save behavior as well as state, you need to either keep the historical code around, use some type of reflection emit trickery to persist the type definition as a loadable assembly, or use dynamic programming tricks that treat data as executable code.

When I have had do versioned serialization before, I normally have custom serialization logic and a “version” attribute on the object – using this I can create a type that I’ve moved and renamed – say SomeClass to Archive.SomeClassV3. You can use Version Tolerant Serialization for this, but I prefer to implement ISerializable and use serialization proxies if this is required. (Well, actually I prefer to avoid this problem altogether!)