Query, Mutation and Subscription Types

Root operation types

The schema defines entry points: fields on Query read data, fields on Mutation change data (executed one after another, in order), and fields on Subscription stream events. Root fields take arguments such as IDs, filters and pagination parameters. Keep root fields focused (user(id:), products(filter:, first:)) and let clients navigate relationships from there rather than adding a root field for every combination.

Root types for the shop

GraphQL SDL.

type Query {
  me: User
  user(id: ID!): User
  product(id: ID!): Product
  products(filter: ProductFilter, first: Int = 20, after: String): ProductConnection!
}

type Mutation {
  addToCart(input: AddToCartInput!): AddToCartPayload!
  placeOrder(input: PlaceOrderInput!): PlaceOrderPayload!
}

type Subscription {
  orderStatusChanged(orderId: ID!): Order!
}

Return nullable single lookups

user(id:) returning User (nullable) lets "not found" be null instead of an error.

Quick check: How are multiple mutation fields in one request executed?

• In parallel, in random order
• Serially, in the order written
• Only the first runs
• They are rejected