How to handle Runtime Polymorphism in Graphql- Java

Question

I was wondering that how can we handle Runtime polymorphism in Graphql Schema file,

@Data
class Parent {
   String libraryName;
}

@Data
class Child extends Parent {
 String bookName;
}

Test class=>

class Test {
 String id;
 Child childObj;
}

Now in normal case Runtime polymorphism will happen and Test.Child will be initialized with Parent class object i.e. Parent prnt = new Child();

e.g. Schema.graphqls

type Test{
  id: String!
  childObj: Child    // Cant assign Parent object
}

// This doesn't work
type Child {
    bookName: String
    libraryName: String
}

type Parent {
    bookName: String
    libraryName: String
}

But in GraphQl Schema file how to mention it ?

Answer 1

In your example, you could define an interface that both the Child and Parent types implement. For example, maybe you'd name it Member and change the type of Test.childObj to Member:

interface Member {
  bookName: String
  libraryName: String
}

type Test {
  id: String!
  childObj: Member    
}

type Child implements Member {
    bookName: String
    libraryName: String
}

type Parent implements Member {
    bookName: String
    libraryName: String
}

Another option might be the extend feature but that doesn't seem to be widely available yet. See this post .