graphql.js

/**
graphql sample query:
{
  event(eventId: "123") {
    days
    eventItems {
      id
      day
  }
}
*/
/**
graphql schema
type Query {
  event(eventId: String!): Event
  happening(happendingId: String!): Happening
}

type Event {
  id: String!
  # unique list of days an eventItem exists for 
  days: [String]
  eventItems: [EventItem]
}
type Happening {
  id: String!
  description: String
  eventItems: [EventItem]
}
*/
const RootResolvers = {
  event(_, args, ctx, info) {
    // option 1: query eventItems here and return them to the child resolver "eventItems" and "days"
    // option 2: pass down eventId to let the child resolver "eventItems" and "days" fetch the data
    
    // pro
      // option 1: eventItems are fetched only once and reused for eventItems + days
      // option 2: logic of how eventItems are fetched is hidden in eventItems resolver and can be reused (eventItems of happening)
      // option 2: child resolvers are only invoked if queried
    // contra
      // option 1: to not unnecessarily fetch eventItems, the info object needs to be parsed to find out if eventItems/days is queried
      // option 1: fetching of eventItems need to be implemented in other (parent) resolvers if necessary
      // option 2: if days and eventItems are queried, both resolvers need to fetch the same data to calc its result
  },
  happening(_, args, ctx, info) {}
}
const Event = {
  id(parent, args, ctx, info) {},
  days(parent, args, ctx, info) {},
  eventItems(parent, args, ctx, info) {}
}
const Happening = {
  id(parent, args, ctx, info) {},
  description(parent, args, ctx, info) {},
  eventItems(parent, args, ctx, info) {}
}