怎么在Spring Data JPA中引入Querydsl?相信很多没有经验的人对此束手无策,为此本文总结了问题出现的原因和解决方法,通过这篇文章希望你能解决这个问题。
基础框架采用Spring Boot、Spring Data JPA、Hibernate。在动态查询中,有一种方式是采用Querydsl的方式。
1、在pom.xml中,引入相关包和配置插件。
(1)引入包(注:不需要版本号,Spring Boot 会自动匹配合适的版本)
<!-- Querydsl相关包 --> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-jpa</artifactId> </dependency> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> </dependency>
(2)配置插件:主要用来生成“查询对象”。
<plugin> <groupId>com.mysema.maven</groupId> <artifactId>maven-apt-plugin</artifactId> <version>1.0.4</version> <executions> <execution> <phase>generate-sources</phase> <goals> <goal>process</goal> </goals> <configuration> <outputDirectory>target/generated-sources</outputDirectory> <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor> </configuration> </execution> </executions> </plugin>
2、设置源文件夹
经过上面pom.xml的配置后,就在 target/generated-sources 文件夹下面自动生成“查询对象”。需要将该文件夹设置成“源文件夹”,以便可以将下面的java文件进行编译使用。
生成的查询对象,都是在原实体(bo)类的名字前,加上 Q 表示。
3、dao中继承接口QueryDslPredicateExecutor
4、在service层使用 Querydsl方式进行是查询,例如:
此文仅作为引入Querydsl的笔记,并不代表作者本人推荐使用Querydsl。就实际应用而言,个人更倾向于使用 JPA Criteria 的方式来实现动态查询,其接口是JpaSpecificationExecutor。
补充:Spring-data-jpa扩展查询 QueryDSL 实践
说明: QueryDSL是以函数连接的方式将SQL调用进行拆分,比较spring data jpa中的criteria查询方法还是简洁了不少。
用例:通过服务调用,使用querydsl进行查询并直接返回DTO对象(自定义传输对象(根据业务需求),注意区别于Entity)
1.创建user与depart表,使用外键进行关联,并插入一些模拟数据。
2.创建sprintboot项目,在pom文件中加入以下依赖:
<dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-jpa</artifactId> </dependency> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> <scope>provided</scope> </dependency>
3.在pom文件中<build>--><plugins>节点下加入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> <dependencies> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> <version>4.1.3</version> </dependency> </dependencies> </plugin>
4.生成相关entity与repository对象,这里以user为例:
注意:repository需要继承 QueryDslPredicateExecutor<T>接口。
5.生成业务传输对象DTO:
package com.test.demo.db; // import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import static javax.persistence.GenerationType.IDENTITY; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.Table; /** * User generated by hbm2java */ @Entity @Table(name = "user", catalog = "testdb") public class User implements java.io.Serializable { private Integer id; private Department department; private String username; public User() { } public User(Department department, String username) { this.department = department; this.username = username; } @Id @GeneratedValue(strategy = IDENTITY) @Column(name = "id", unique = true, nullable = false) public Integer getId() { return this.id; } public void setId(Integer id) { this.id = id; } @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "fk_depart") public Department getDepartment() { return this.department; } public void setDepartment(Department department) { this.department = department; } @Column(name = "username", length = 45) public String getUsername() { return this.username; } public void setUsername(String username) { this.username = username; } }
package com.test.demo.repo; import org.springframework.data.jpa.repository.JpaRepository; import org.springframework.data.jpa.repository.JpaSpecificationExecutor; import org.springframework.data.querydsl.QueryDslPredicateExecutor; import org.springframework.stereotype.Repository; import com.test.demo.db.User; @Repository public interface UserRepository extends QueryDslPredicateExecutor<User>, JpaRepository<User, Integer>,JpaSpecificationExecutor<User>{ }
注意:repository需要继承 QueryDslPredicateExecutor<T>接口。
5.生成业务传输对象DTO:
package com.test.demo.controller; import com.querydsl.core.annotations.QueryProjection; import lombok.Data; @SuppressWarnings("unused") public @Data class UserDTO { private String username; private String departname; }
6.创建controller进行测试:
package com.test.demo.controller; import java.util.HashMap; import java.util.List; import java.util.Map; import javax.annotation.PostConstruct; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestParam; import org.springframework.web.bind.annotation.RestController; import com.querydsl.core.types.Projections; import com.querydsl.core.types.dsl.BooleanExpression; import com.querydsl.jpa.impl.JPAQuery; import com.querydsl.jpa.impl.JPAQueryFactory; import com.test.demo.db.QUser; import com.test.demo.repo.UserRepository; @RestController @RequestMapping("/") public class TestController { @Autowired UserRepository userRepo; @Autowired @PersistenceContext EntityManager em; private JPAQueryFactory queryFactory; @PostConstruct public void init() { queryFactory = new JPAQueryFactory(em); } @RequestMapping("/users") Object getUsers(@RequestParam(value = "page", required = false, defaultValue = "1") Integer page, @RequestParam(value = "size", required = false, defaultValue = "10") Integer size, @RequestParam(value = "name", required = false) String name, @RequestParam(value = "depart", required = false) String depart) { QUser user = QUser.user; JPAQuery<UserDTO> query = queryFactory .select(Projections.bean(UserDTO.class, user.username, user.department.name.as("departname"))) .from(user); BooleanExpression pre = null; if (name!=null && !name.isEmpty()) { pre = user.username.startsWith(name); } if (depart!=null && !depart.isEmpty()) { pre = user.department.name.startsWith(depart); } query.where(pre); query.limit(size); query.offset((page-1)*size); List<UserDTO> result = query.fetch(); Map<String, Object> map = new HashMap<>(); map.put("total", userRepo.count(pre)); map.put("data", result); return map; } }
注:这里就是使用querydsl进行查询,并直接转换需要的属性至DTO。并且代码中的pre是可以根据参数动态拼接的。
7.测试结果:
这是查询日志:
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