what's the right way to do polymorphism with protocol buffers?

Question

I\'m trying to long-term serialize a bunch of objects related by a strong class hierarchy in java, and I\'d like to use protocol buffers to do it due to their simplicity, pe

Answer 1

There are a few techniques for implementing polymorphism. I try to cover them all here: Protocol Buffer Polymorphism

My preferred approach uses nested extensions:

message Animal
{
    extensions 100 to max;

    enum Type
    {
        Cat = 1;
        Dog = 2;
    }

    required Type type = 1;
}

message Cat
{
    extend Animal
    {
        required Cat animal = 100; // Unique Animal extension number
    }

    // These fields can use the full number range.
    optional bool declawed = 1;
}

message Dog
{
    extend Animal
    {
        required Dog animal = 101; // Unique Animal extension number
    }

    // These fields can use the full number range.
    optional uint32 bones_buried = 1;
}