Can extracting a base class break binary serialisation

Question

If I have a class with a number of fields, and I serialise it using binary serialisation.

I then extract a base class and move some of the fields from the class into the base class. Eg.

class Class
{
     int field1;
     string field2;
}

Is changed to

class Class : BaseClass
{
     int field1;
}

class BaseClass
{
     string field2;
}

Is it possible for this to break serialisation in any way - i.e. will it always be possible to deserialise old versions of Class into new versions of Class and vice versa.

Experiments I performed indicated that this is fine, but if somebody knows of any edge cases where this wouldn't work, that would obviously be great before I put this into production code.

Answer 1

EDIT: There is a problem while deserializing: the member "field1" will not be properly deserialized.

1) Serialized person:

var person = new Employee()
            { 
                Name = "Mark Zuckerberg",
                Salary = 1000
            };

var bf = new BinaryFormatter();
bf.Serialize(new FileStream("C:\\TEMP\\test.dat", FileMode.Create), person);


[Serializable]
public class Employee
{
  public string Name { get; set; }
  public decimal Salary { get; set; }
}

2) Changed class structure

[Serializable]
public abstract class Person
{
  public string Name { get; set; }           
}

[Serializable]
public class Employee : Person
{            
  public decimal Salary { get; set; }
}

3) Deserialized: Name is null

---

Original Answer:

Assuming you are using the BinaryFormatter, this article does not mention anything about it, so I guess it's fine (EDIT: It's NOT fine).

Here are some best practices to follow generally (also extracted from above article):

• Never remove a serialized field.
• Never apply the NonSerializedAttribute attribute to a field if the attribute was not applied to the field in the previous version.
• Never change the name or the type of a serialized field.
• When adding a new serialized field, apply the OptionalFieldAttribute attribute.
• When removing a NonSerializedAttribute attribute from a field (that was not serializable in a previous version), apply the OptionalFieldAttribute attribute.
• For all optional fields, set meaningful defaults using the serialization callbacks unless 0 or null as defaults are acceptable.

To ensure that a type will be compatible with future serialization engines, follow these guidelines:

• Always set the VersionAdded property on the OptionalFieldAttribute attribute correctly.
• Avoid branched versioning.