custom errors in graphql mutation

examples

// query
mutation {
  createUser(user: {username: "John Doe", email: "john.doe@test"}) {
    user {
      email
      username
    }
    errors {
      key
      message
    }
  }
}

// response
{
  data {
    createUser {
      user: null,
      errors: [{
        key: "email",
        message: "Email address is invalid"
      }]
    }
  }
}

types

type Mutation {
  createUser(user: CreateUserInput!): UserMutationResponse
}

input CreateUserInput {
  username
  email
}

type CreateUserMutationResponse {
  user: User
  errors: [ServiceError]
}

type User {
  email: String
  username: String
}

type ServiceError {
  key: String
  message: String
}