[Play Json] How to ignore sub-type during serialization

[trantienduchn (Duc Tran Tien)]

I have following classes

trait Parent
case class FirstChild extends Parent
case class SecondChild extends Parent

The results I got after serializing FirstChild and SecondChild contain a json field _type=com.abc.FirstChild.

I don’t want to expose the internal structure to rest clients of course, So how can I ignore that _type field ?