Unions

A union type is defined as a list of object types:

union SearchResult = User | Post

type User {
  name: String
  profilePic: Url
}

type Post {
  text: String
  upvotes: Int
}

When a field is typed as a union, its value can be any of the objects listed in the union definition. So the below search query returns a list of User and Post objects.

type Query {
  search(term: String): SearchResult
}

query {
  search(term: "John") {
    ... on User {
      name
    }
    ... on Post {
      text
    }
  }
}

Since unions don’t guarantee any fields in common, any field we select has to be inside a fragment (which has a specific object type).