spring-boot 中使用graphql的正确姿势

在spring-boot中使用graphql

首先构建spring-boot项目，pom.xml文件中加入

<dependency>
  <groupId>com.graphql-java-kickstart</groupId>
  <artifactId>graphql-java-tools</artifactId>
  <version>5.4.0</version>
</dependency>
<!-- graphql -->
<dependency>
   <groupId>com.graphql-java</groupId>
   <artifactId>graphql-spring-boot-starter</artifactId>
   <version>5.0.2</version>
</dependency>
<!-- 这个是graphiql，跟上面的不一样 -->
 <dependency>
    <groupId>com.graphql-java</groupId>
    <artifactId>graphiql-spring-boot-starter</artifactId>
    <version>5.0.2</version>
</dependency>

接着定义graphql的schema，在resources目录下任意位置的*.graphqls文件都会被扫描到，作为graphql 的schema。

这里在resources下先建一个文件夹/graphql，建立schema文件

schema.graphqls

type Query {
    user(nickname: String): User
    users: [User]
    article(title: String!): Article
}
type Mutation {
    addUser(mail: String!, nickname: String!, password: String!): User
    addArticle(title: String!, content: String!, authorId: String!): Article
}
type User {
    id: String!
    mail: String!
    nickname: String!
    password: String!
    description: String
}

type Article {
    id: String!
    author: User!
    title: String!
    content: String!
    createBy: String
    thumbUp: Int
}

Resolver 和数据类

GraphQL Java Tools可以将schema中定义的类型的属性与java对象的属性或方法对应起来。即上面的User类型，可以使用一个类与之对应

public class User {
    @Id
    private String id;
    private String nickname;
    private String mail;
    private String password;
    private String description;
    // 构造器，getter和setter
}

但是在Article类型中author的属性是User，我们该如何解决呢？

这时我们可以使用一个GraphQLResolver指定某个类型的解析

@Component
public class ArticleResolver implements GraphQLResolver<Article> {
    private final UserRepository userRepository;

    public ArticleResolver(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User author(Article article) {
        return userRepository.findById(article.getAuthorId()).get();
    }
}

指定Article类型的解析方式，其中标量类型可以直接从Aritcle的java类属性中获取，所以不必写方法，对于author这个属性，其类型为User，我们指定author()方法进行解析。

那么到底type Article {...}schema里面的属性怎么解析呢？是与数据类进行映射，还是与resolver中的方法进行映射？

官网上给出了映射的优先级:

首先是resolver

method 属性名(...)
method is属性名(...)
method get属性名(...)
method getField属性名(...)

其次是Data Class(即与类型对应的java类)

method 属性名(...)
method is属性名(...)
method get属性名(...)
method getField属性名(...)
field 属性名

所以首先在ArticleResolver中查找author的映射，找不到的属性则一致向下找到属性的java类的get方法/属性本身。

另外，要给Query和Mutation至少创建一个Resolver

@Component
public class QueryResolver implements GraphQLQueryResolver {

    private final UserRepository userRepository;
    private final ArticleRepository articleRepository;

    public QueryResolver(UserRepository userRepository, ArticleRepository articleRepository) {
        this.userRepository = userRepository;
        this.articleRepository = articleRepository;
    }

    public Article article(String title) {
        return articleRepository.findArticleByTitle(title);
    }

    public User user(String nickname) {
        return userRepository.findUserByNickname(nickname);
    }

    public List<User> users() {
        return userRepository.findAll();
    }
}

@Component
public class MutationResolver implements GraphQLQueryResolver, GraphQLMutationResolver {

    private final ArticleRepository articleRepository;
    private final UserRepository userRepository;
    private final BCryptPasswordEncoder encoder;

    public MutationResolver(ArticleRepository articleRepository, UserRepository userRepository, BCryptPasswordEncoder encoder) {
        this.articleRepository = articleRepository;
        this.userRepository = userRepository;
        this.encoder = encoder;
    }
    public User addUser(String mail, String nickname, String password) {
        if(userRepository.findUserByNickname(nickname) != null){
            return null;
        }
        return userRepository.save(User.builder()
                .nickname(nickname)
                .mail(mail)
                .password(encoder.encode(password))
                .build());
    }

    public  Article addArticle(String title, String content, String authorId) {
        if(!userRepository.findById(authorId).isPresent()){
            return null;
        }
        return articleRepository.save(Article.builder()
                .authorId(authorId)
                .title(title)
                .content(content)
                .createBy(new Date())
                .thumbUp(0)
                .build());
    }

}

这里使用mongodb存储数据。

运行，在http://localhost:8080/graphiql 中进行操作

具体代码戳这里