graphql-schema-design

# GraphQL Schema Design

Apply GraphQL schema design principles to create well-structured,
maintainable, and scalable GraphQL APIs. This skill covers the type
system, Schema Definition Language (SDL), field design patterns,
pagination strategies, directives, and schema evolution techniques.

## Core Type System

### Object Types

Object types are the fundamental building blocks of GraphQL schemas.
Each object type represents a kind of object you can fetch from your
service, and what fields it has.

```graphql
type User {
  id: ID!
  username: String!
  email: String!
  createdAt: DateTime!
  posts: [Post!]!
  profile: Profile
}

type Post {
  id: ID!
  title: String!
  content: String!
  author: User!
  publishedAt: DateTime
  tags: [String!]!
}
```

### Interface Types

Interfaces define abstract types that multiple object types can
implement. Use interfaces when multiple types share common fields.

```graphql
interface Node {
  id: ID!
  createdAt: DateTime!
  updatedAt: DateTime!
}

interface Timestamped {
  createdAt: DateTime!
  updatedAt: DateTime!
}

type Article implements Node & Timestamped {
  id: ID!
  createdAt: DateTime!
  updatedAt: DateTime!
  title: String!
  content: String!
  author: User!
}

type Comment implements Node & Timestamped {
  id: ID!
  createdAt: DateTime!
  updatedAt: DateTime!
  text: String!
  author: User!
  post: Post!
}
```

### Union Types

Union types represent values that could be one of several object types.
Use unions when a field can return different types without shared
fields.

```graphql
union SearchResult = Article | User | Tag | Comment

type Query {
  search(query: String!): [SearchResult!]!
}

# Query example
query {
  search(query: "graphql") {
    __typename
    ... on Article {
      title
      content
    }
    ... on User {
      username
      email
    }
    ... on Tag {
      name
      count
    }
  }
}
```

### Enum Types

Enums define a specific set of allowed values for a field. Use enums
for fields with