Enums, Interfaces, Unions and Inputs

Richer types

Enums restrict a field to fixed values (OrderStatus). Interfaces define common fields that several types implement (Node { id: ID! }), and unions say a field returns one of several unrelated types (SearchResult = Product | User); clients use inline fragments to pick type-specific fields. Input types describe structured arguments for mutations and filters; output object types cannot be used as inputs.

Enum, interface, union and input

GraphQL SDL.

enum OrderStatus { PENDING PAID SHIPPED CANCELLED }

interface Node { id: ID! }

type Product implements Node {
  id: ID!
  name: String!
  price: Money!
}

union SearchResult = Product | User

input ProductFilter {
  category: String
  maxPrice: Float
  inStock: Boolean
}

input AddToCartInput {
  productId: ID!
  quantity: Int! = 1
}

Use enums for closed sets

Enums give clients autocomplete and validation; strings invite typos.

Quick check: Which type describes structured arguments to a mutation?

• A subscription
• A union
• An interface
• An input type