wrapper-types-example.js

const typeDefs = gql`
  # define wrapper result type that could return either
  # the added Event on success, or an array of Errors 
  # on error. Notice both fields are nullable. 
  type AddEventResult {
    event: Event
    validationErrors: [FieldValidationError!]
  }

  # define how you want errors to be represented. This
  # can be as complex as your app requires
  type FieldValidationError {
    field: String!
    message: String!
    (... any other fields you need)
  }

  input EventInput {
    name: String!
    date: Date!
    capacity: Int!
    photoUrl: String!
  }

  type Mutation {
    addEvent(event: EventInput!): AddEventResult!
  }
`;