Querydsl与SpringBoot集成

Querydsl为大多数数据库提供了一种基于Java的类型安全，类SQL的查询方式。相比JPA，Querydsl能提供更加强大的查询方式，比如关联查询。相比MyBatis，Querydsl省去了XML文件或者注解SQL的麻烦，直接通过流式API的方式进行调用。

除了支持关系型数据库之外，Querydsl同样支持一下存储

• MongoDB
• Lucene
• Collections
• Spatial
• JDO

接下来通过H2+JPA的方式介绍Querydsl的基本使用（为了演示采用H2数据库）

一、创建项目，添加依赖

本文采用Spring Boot快速搭建项目，并在pom.xml中添加以下依赖

				<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-apt</artifactId>
            <version>4.3.1</version>
        </dependency>
        <dependency>
            <groupId>com.querydsl</groupId>
            <artifactId>querydsl-jpa</artifactId>
            <version>4.3.1</version>
        </dependency>
        
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>com.mysema.maven</groupId>
                <artifactId>apt-maven-plugin</artifactId>
                <version>1.1.3</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>process</goal>
                        </goals>
                        <configuration>
                            <outputDirectory>target/generated-sources/java</outputDirectory>
                            <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

注意
当在项目中使用的是JPA的注解（ javax.persistence.Entity）的时候，需要使用JPAAnnotationProcessor生成相关的查询类，如果使用的是Hibernate注解的时候，需要将JPAAnnotationProcessor替换成com.querydsl.apt.hibernate.HibernateAnnotationProcessor。

二、创建实体类

@Entity
public class User {
    @Id
    private Integer id;
    private String name;
		// 省略getter, setter等方法
}

@Entity
public class UserInfo {
    @Id
    private Integer userId;
    private Integer sex;
}

实体类创建完成之后，重新编译项目

mvn clean package

在target/generated-sources/java目录中可以看到编译后生成的查询类（Q开头的类，例如QUser， QUserInfo）

三、测试

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class QuerydslTests {
    @Autowired
    private EntityManager entityManager;
    private JPAQueryFactory queryFactory;
    private QUser qUser;
    private QUserInfo qUserInfo;

    @BeforeEach
    void setUp() {
        queryFactory = new JPAQueryFactory(entityManager);
        qUser = QUser.user;
        qUserInfo = QUserInfo.userInfo;
    }

    @Test
    void simpleQuery() {
        User user = queryFactory.selectFrom(qUser)
                .where(qUser.name.eq("XiaoMing"))
                .fetchOne();
        Assertions.assertNotNull(user);
        Assertions.assertEquals("XiaoMing", user.getName());
    }

    @Test
    void simpleQueryFields() {
        String name = queryFactory.selectFrom(qUser)
                .select(qUser.name)
                .where(qUser.name.eq("XiaoMing"))
                .fetchOne();
        Assertions.assertNotNull(name);
        Assertions.assertEquals("XiaoMing", name);
    }

    @Test
    void join() {
        Tuple tuple = queryFactory.selectFrom(qUser)
                .select(qUser.id, qUser.name, qUserInfo.sex)
                .innerJoin(qUserInfo).on(qUserInfo.userId.eq(qUser.id))
                .where(qUser.name.eq("XiaoMing"))
                .fetchOne();
        Assertions.assertNotNull(tuple);
        Assertions.assertNotEquals(0, tuple.size());
        Integer userId = tuple.get(0, Integer.class);
        String name = tuple.get(1, String.class);
        Integer sex = tuple.get(2, Integer.class);
        Assertions.assertEquals(1, userId);
        Assertions.assertEquals("XiaoMing", name);
        Assertions.assertEquals(0, sex);
    }
}

最后附上数据库初始化脚本

insert into `user` (id, name) values (1, 'XiaoMing');
insert into `user` (id, name) values (2, 'XiaoHong');

insert into `user_info` (user_id, sex) values (1, 0);
insert into `user_info` (user_id, sex) values (2, 1);