Object Types, Scalars and Nullability

Fields, lists and non-null

An object type has fields, each with a type. Built-in scalars are Int, Float, String, Boolean and ID; custom scalars such as DateTime can be added. ! marks a field as non-null and [Type] is a list, so [Order!]! is a non-null list of non-null orders. Fields can take arguments, and descriptions in triple quotes become documentation. Design types around the client's domain language, not your database tables.

The contract between client and server

The Schema Definition Language (SDL) describes types, fields and operations clients can use.

A shop schema

GraphQL SDL.

"""A registered customer."""
type User {
  id: ID!
  name: String!
  email: String!
  orders(first: Int = 10, after: String): OrderConnection!
}

type Order {
  id: ID!
  placedAt: DateTime!
  status: OrderStatus!
  total: Money!
  items: [OrderItem!]!
}

type OrderItem {
  product: Product!
  quantity: Int!
}

scalar DateTime

Be deliberate with non-null

Non-null fields are a promise; if a resolver fails, the null bubbles up to the nearest nullable parent, possibly wiping out more data than expected.

Quick check: What does [Order!]! mean?

• An optional list of optional orders
• A non-null list whose items are non-null orders
• Exactly one order
• A map of orders