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Spring Boot 4 Complete Guide · Lesson

Schema-First Design and Type Mapping

Define a GraphQL schema and map types, queries, and mutations to Java controller methods.

Schema-First in Spring for GraphQL

Spring for GraphQL is schema-first: you describe your API in a .graphql Schema Definition Language (SDL) file, and your Java code maps onto it.

  • The schema is the single source of truth for the API contract.
  • Clients ask for exactly the fields they need.
  • Your controllers provide the data behind each field.

By convention, Spring Boot auto-discovers .graphqls / .graphql files under src/main/resources/graphql/.

Defining Object Types in SDL

A GraphQL object type describes the shape of an entity. Each field has a name and a type.

  • ID, String, Int, Float, Boolean are the built-in scalars.
  • A trailing ! marks a field as non-null.
  • [Type] denotes a list.

Place this in src/main/resources/graphql/schema.graphqls.

type Book {
    id: ID!
    title: String!
    pageCount: Int
    author: Author!
}

type Author {
    id: ID!
    name: String!
    books: [Book!]!
}

All lessons in this course

  1. Schema-First Design and Type Mapping
  2. Data Fetchers and Argument Binding
  3. Solving N+1 with Batch Loaders
  4. Subscriptions, Errors, and Schema Security
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