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

Jon's solution is correct and working but pretty weird (for me). But Protocol Buffers is quite simple, so You can do something like that:

enum Type {
    FOO = 0;
    BAR = 1;
  }

message Foo {
  required Type type = 1;
}

message Bar {
  required Type type = 1;
  required string text = 2;
}

Basically message Bar extends message Foo (from practical side of course). Implementation in Java is simple too:

Bar bar = Bar.newBuilder().setType(Type.BAR).setText("example").build();
byte[] data = bar.toByteArray();

----

Foo foo = Foo.parseFrom(data);
if(foo.getType() == Type.BAR){
   Bar bar = Bar.parseFrom(data);
   System.out.println(bar.getText());
}

I known, it's not an elegant solution, but it's simple and logical.