Extending

All named types can be extended in some way. We might extend types when we’re defining our schema across multiple files, or if we’re modifying a schema defined by someone else. Here are a couple examples:

type Query { 
  messages: [String]
}

type Direction {
  NORTH
  EAST
  SOUTH
  WEST
}

extend type Query {
  lastMessage: String
}

extend enum Direction {
  SOUTHEAST
  SOUTHWEST
  NORTHEAST
  NORTHWEST
}

First we add a root query field, and then we add four more possible values for the Direction enum.