Question

Having a problem while deserializing a number of objects stored as BLOBs in a MySQL database.

Each object class has its own deserialize function.

Class1 c1Holder = (Class1)binFormatter.Deserialize(memStream);

Works fine, but then …

Class2 c2Holder = (Class2)binFormatter.Deserialize(memStream);

…calls the Class1 deserialize function. When I step through it using the VS 2010 debugger it will call the correct function on the 2nd attempt.
Also…

Class3 c3Holder = (Class3)binFormatter.Deserialize(memStream);

…calls the Class1 deserialize function, then the Class2 function and finally the correct function.

Any ideas?

Answer 1

From the comments:

Unable to cast object of type ‘Assembly.Class1’ to type ‘Assembly.Class4’.

Unable to cast object of type ‘Assembly.Class2’ to type ‘Assembly.Class4’.

Unable to cast object of type ‘Assembly.Class3’ to type ‘Assembly.Class4’.

This suggests that you are simply expecting the data to be a different type than it actually is. The point of BinaryFormatter is that if you serialize a Class7, then it will deserialize as a class7. With other serializers, you often need to tell it what to deserialize it as, allowing different types to be interchangeable as long as they look similar.

So with BinaryFormatter: if you want to get a Class2, serialize a Class2.

To be clear, the following:

Class2 c2Holder = (Class2)binFormatter.Deserialize(memStream);

does not say "deserialize this as a Class2" – it is more like:

object tmp = binFormatter.Deserialize(memStream);
Class2 c2Holder = (Class2)tmp;

i.e. "serialize it into whatever it is, then cast that as a Class2". If it isnt a Class2 it will fail. This isn’t a conversion etc – is is a type-check only.

If you want advice on serialization that works with similar-but-different typed, let me know.