GraphQL APIs with Spring Boot · レッスン

インターフェースとUnion型の実装

インターフェースとUnion型を活用し、柔軟でポリモーフィックなスキーマを設計します。

「インターフェースとUnion型の実装」はCoddyKit上の無料GraphQL APIs with Spring Bootレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはGraphQL APIs with Spring Boot学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 GraphQL APIs with Spring Bootコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Flexible Schemas with Polymorphism

GraphQL allows you to design highly flexible APIs. Sometimes, you need a field that can return different types of objects, or you want to define a shared set of fields that multiple types must implement. This is where polymorphism comes in.

We'll explore two key concepts for achieving this: Interfaces and Union Types.

Understanding GraphQL Interfaces

Imagine you have different types of media, like a Book and a Movie. Both might have a title and a releaseYear. Instead of duplicating these fields, you can define an Interface.

An interface is a contract that specifies a set of fields that any type implementing it must include. It's like a blueprint for common functionality.

Defining an Interface in SDL

In GraphQL's Schema Definition Language (SDL), an interface is defined using the interface keyword. Here, we define a Media interface that both Book and Movie will share.

interface Media {
  id: ID!
  title: String!
  releaseYear: Int
}

Types Implementing an Interface

Now, let's make our Book and Movie types implement the Media interface. They must include all fields defined by Media, and can add their own unique fields. Notice the implements keyword.

type Book implements Media {
  id: ID!
  title: String!
  releaseYear: Int
  author: String
  pages: Int
}

type Movie implements Media {
  id: ID!
  title: String!
  releaseYear: Int
  director: String
  durationMinutes: Int
}

Resolvers for Interfaces

When you query a field that returns an interface type, Spring GraphQL automatically resolves the concrete type based on the data. You usually create Java data classes that implement a common Java interface, and Spring GraphQL handles the rest. Try running this example:

package com.coddykit.graphql;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.graphql.data.method.annotation.QueryMapping;
import org.springframework.stereotype.Controller;

import java.util.List;
import java.util.ArrayList;

@SpringBootApplication
public class GraphqlApp {
    public static void main(String[] args) {
        SpringApplication.run(GraphqlApp.class, args);
    }
}

interface Media {
    String getId();
    String getTitle();
    Integer getReleaseYear();
}

record Book(String id, String title, Integer releaseYear, String author, Integer pages) implements Media {}
record Movie(String id, String title, Integer releaseYear, String director, Integer durationMinutes) implements Media {}

@Controller
class MediaController {

    @QueryMapping
    public List<Media> allMedia() {
        List<Media> mediaList = new ArrayList<>();
        mediaList.add(new Book("b1", "The Hitchhiker's Guide", 1979, "Douglas Adams", 193));
        mediaList.add(new Movie("m1", "Inception", 2010, "Christopher Nolan", 148));
        return mediaList;
    }
}

Exploring GraphQL Union Types

While interfaces ensure types share common fields, Union Types allow a field to return one of several distinct types, without requiring them to share any common fields. Think of it as an 'either-or' situation. For example, a search result might be a Product OR a User.

Schema Definition for Unions

In SDL, union types are defined using the union keyword, followed by the types it can represent, separated by a vertical bar |. Here's a SearchResult union that can be either a Book or a Movie.

union SearchResult = Book | Movie

Resolvers for Union Types

When a field returns a union type, Spring GraphQL needs to know which concrete type it is. For Java, you simply return an instance of one of the types defined in the union. Spring GraphQL automatically adds the __typename field for clients to distinguish. Try running this example:

package com.coddykit.graphql;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.graphql.data.method.annotation.Argument;
import org.springframework.graphql.data.method.annotation.QueryMapping;
import org.springframework.stereotype.Controller;

@SpringBootApplication
public class GraphqlApp {
    public static void main(String[] args) {
        SpringApplication.run(GraphqlApp.class, args);
    }
}

record Book(String id, String title, Integer releaseYear, String author, Integer pages) {}
record Movie(String id, String title, Integer releaseYear, String director, Integer durationMinutes) {}

@Controller
class SearchController {

    @QueryMapping
    public Object search(@Argument String query) {
        if (query.equalsIgnoreCase("inception")) {
            return new Movie("m1", "Inception", 2010, "Christopher Nolan", 148);
        } else if (query.equalsIgnoreCase("hitchhiker")) {
            return new Book("b1", "The Hitchhiker's Guide", 1979, "Douglas Adams", 193);
        }
        return null;
    }
}

Choosing Between Interfaces and Unions

Both interfaces and unions offer polymorphism, but they serve different purposes:

Interfaces: Use when multiple types share a common set of fields and behavior. They enforce a contract.
Union Types: Use when a field can return one of several distinct types that do not necessarily share any common fields. It's about 'either A or B or C'.

Interfaces vs. Unions Quiz

You are designing a GraphQL API. You need a field that can return either a Photo object or a Video object. These two types have completely different fields and do not share any common properties. Which GraphQL schema feature is best suited for this scenario?

Recap: Flexible Schemas

You've learned how GraphQL Interfaces and Union Types enable flexible and polymorphic schema designs. Interfaces define a contract for common fields, while Union Types allow a field to return one of several distinct types. These tools are crucial for building robust and adaptable GraphQL APIs.

Next, you'll explore Input Types to streamline mutation arguments.

よくある質問

「インターフェースとUnion型の実装」レッスンは無料ですか？

はい。「インターフェースとUnion型の実装」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、GraphQL APIs with Spring Bootコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 GraphQL APIs with Spring Bootコースには全4レッスンが含まれています。

「インターフェースとUnion型の実装」で何を学びますか？

インターフェースとUnion型を活用し、柔軟でポリモーフィックなスキーマを設計します。ブラウザで直接実行するハンズオンコードでGraphQL APIs with Spring Bootを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

GraphQL APIs with Spring Bootを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのGraphQL APIs with Spring Bootは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「インターフェースとUnion型の実装」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このGraphQL APIs with Spring Bootレッスンでコードを書いて実行できますか？

はい。すべてのGraphQL APIs with Spring Bootレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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