前言
JPA中可以通过设置实体的导航属性 + JPQL完成复杂的多表查询，简化SQL的编写。
示例
建表语句
- Table
CREATE TABLE `school` (
`id` int(11) DEFAULT NULL,
`name` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `student` (
`id` int(11) DEFAULT NULL,
`name` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `school_student` (
`id` int(11) DEFAULT NULL,
`school_id` int(11) DEFAULT NULL,
`student_id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
- 上述表中Studen和School呈现多对多关系
Entity实体
- School.java
@Entity
@Setter
@Getter
public class School {
@Id
private Integer id;
private String name;
/**
* 多对多关系配置
*/
@ManyToMany(fetch = FetchType.LAZY, mappedBy = "schoolList")
private List<Student> studentList;
}
- Student.java
@Entity
public class Student {
@Id
private Integer id;
private String name;
/**
* 多对多关系配置
*/
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "school_student",
joinColumns = @JoinColumn(name = "student_id"),
inverseJoinColumns = @JoinColumn(name = "school_id"))
private List<School> schoolList;
}
JPQL多表查询
- 在这里，通过Studen ID 查询出关联的 School
- 常规SQL关联查询：
select
sch.id ,
sch.name
from
school sch
inner join
school_student ss
on sch.id = ss.school_id
inner join
student stu
on ss.student_id = stu.id
where
stu.id = 1
- JPQL多表查询：
@Query("select s from School s " +
"join s.studentList ss " +
"where ss.id = :id ")
完整代码
- TestController.java
@RestController
@RequestMapping("/test")
public class TestController {
@Autowired
private StudentRepository studentRepository;
@GetMapping(value = "/test")
public List<Student> test(@RequestParam Integer id){
return studentRepository.findStudenBySchool(id);
}
}
- StudentRepository.java
@Repository
public interface StudentRepository extends JpaRepository<School, Long> {
@Query("select s from School s " +
"join s.studentList ss " +
"where ss.id = :id ")
List<Student> findStudenBySchool(Integer id);
}
调用结果
