SpringBoot-SpringData-ManyToMany
前面我们说了SpringData的@OneToOne : SpringBoot-SpringData-oneToOne
这节说一下@ManyToMany
多对多映射:一方实例可以获取多个对方实例引用,反之亦然
模型
以学生选课为模型,学生和选修课为多对多关系
项目结构
学生类Student及StudentRepository
课程类Course及CourseRepository
测试类ManyToManyTest
Domain
学生类
@Entity
@Table(name = "student")
public class Student {
private String pid;
private String studentName;
private Set course; //选修课程
public Student() {
}
public Student(String pid, String studentName, Set course) {
this.pid = pid;
this.studentName = studentName;
this.course = course;
}
@Id
@Column(name = "pid", unique = true, nullable = false, length = 32)
@GeneratedValue(generator = "generator")
@GenericGenerator(name = "generator", strategy = "uuid")
public String getPid() {
return pid;
}
@Column(name = "student_name", unique = true, length = 64)
public String getStudentName() {
return studentName;
}
/**
* Hibernate 会自动创建一张关系表stu_cou， 里边有俩字段stu_id和cou_idfen分别为两表主键
*
* @return
*/
@ManyToMany(cascade = {CascadeType.MERGE, CascadeType.REFRESH}, fetch = FetchType.EAGER)
@JoinTable(name = "stu_cou", joinColumns = {@JoinColumn(name = "stu_id")}, inverseJoinColumns = {@JoinColumn(name = "cou_id")})
public Set getCourse() {
return course;
}
public void setPid(String pid) {
this.pid = pid;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public void setCourse(Set course) {
this.course = course;
}
} 课程类
@Entity
@Table(name = "course")
public class Course implements java.io.Serializable {
private static final long serialVersionUID = 6398143635533582335L;
private String pid;
private String courseName;// 课程名称
private Set Student; // 选修课程学生
public Course() {
}
public Course(String pid, String courseName, Set student) {
this.pid = pid;
this.courseName = courseName;
this.Student = student;
}
@Id
@Column(name = "pid", unique = true, nullable = false, length = 32)
@GeneratedValue(generator = "generator")
@GenericGenerator(name = "generator", strategy = "uuid")
public String getPid() {
return pid;
}
@Column(name = "course_name", unique = true, length = 64)
public String getCourseName() {
return courseName;
}
//mappedBy :
// 表示当前所在表和 Student 的关系是定义在 Student 里面的 course 这个成员上面的，
// 他表示此表是一对一关系中的从表，也就是关系是在 Student 表中维护的，
// Student 表是关系的维护者，有主导权，它有个外键指向 course (Student 中的 getCourse() )
@ManyToMany(fetch = FetchType.EAGER, mappedBy = "course")
//NotFound : 意思是找不到引用的外键数据时忽略，NotFound默认是exception
@NotFound(action = NotFoundAction.IGNORE)
public Set getStudent() {
return Student;
}
public void setPid(String pid) {
this.pid = pid;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public void setStudent(Set student) {
Student = student;
}
} DAO
public interface StudentRepository extends JpaRepository<Student, Long> {
Student findByStudentName(String name);
}
public interface CourseRepository extends JpaRepository<Course, Long> {
Course findByCourseName(String name);
}application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=123
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.jpa.properties.hibernate.hbm2ddl.auto=create-drop
spring.jpa.show-sql=true测试Test
@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(DemoApplication.class)
public class ManyToManyTest {
@Autowired
CourseRepository courseRepository;
@Autowired
StudentRepository studentRepository;
@Before
public void testData(){
//Course
Course course1 = new Course();
course1.setCourseName("course1");
Course course2 = new Course();
course2.setCourseName("course2");
Course course3 = new Course();
course3.setCourseName("course3");
courseRepository.save(course1);
courseRepository.save(course2);
courseRepository.save(course3);
//Student
Student student1 = new Student();
student1.setStudentName("Student1");
Student student2 = new Student();
student2.setStudentName("Student2");
Student student3 = new Student();
student3.setStudentName("Student3");
// 学生1 选修课程12
Set courses = null;
courses = new HashSet<>();
courses.add(course1);
courses.add(course2);
student1.setCourse(courses);
studentRepository.save(student1);
// 学生2 选修课程23
courses = new HashSet<>();
courses.add(course2);
courses.add(course3);
student2.setCourse(courses);
studentRepository.save(student2);
}
@Test
public void test() throws Exception {
//取学生
Student student1 = studentRepository.findByStudentName("Student1");
System.out.print("student1.getStudentName()" + student1.getStudentName());
//取课程
Course course2 = courseRepository.findByCourseName("course2");
System.out.print("course2.getCourseName()" + course2.getCourseName());
}
} 测试结果
取学生获取课程实例:
取课程获取学生实例
SpringData自动创建的数据库
-- ----------------------------
-- Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
`pid` varchar(32) NOT NULL,
`course_name` varchar(64) DEFAULT NULL,
PRIMARY KEY (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('8a8c32c257d67b2a0157d67b2fe90000', 'course1'), ('8a8c32c257d67b2a0157d67b30350001', 'course2'), ('8a8c32c257d67b2a0157d67b30380002', 'course3');
COMMIT;
-- ----------------------------
-- Table structure for `stu_cou`
-- ----------------------------
DROP TABLE IF EXISTS `stu_cou`;
CREATE TABLE `stu_cou` (
`stu_id` varchar(32) NOT NULL,
`cou_id` varchar(32) NOT NULL,
PRIMARY KEY (`stu_id`,`cou_id`),
KEY `FK_fd2i9jhyx88ktcbudlprem9y0` (`cou_id`),
CONSTRAINT `FK_fd2i9jhyx88ktcbudlprem9y0` FOREIGN KEY (`cou_id`) REFERENCES `course` (`pid`),
CONSTRAINT `FK_k71umpbvqf7722foi4l5d97g9` FOREIGN KEY (`stu_id`) REFERENCES `student` (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of `stu_cou`
-- ----------------------------
BEGIN;
INSERT INTO `stu_cou` VALUES ('8a8c32c257d67b2a0157d67bbc5c0003', '8a8c32c257d67b2a0157d67b2fe90000'), ('8a8c32c257d67b2a0157d67bbc5c0003', '8a8c32c257d67b2a0157d67b30350001'), ('8a8c32c257d67b2a0157d67c6f0c0004', '8a8c32c257d67b2a0157d67b30350001'), ('8a8c32c257d67b2a0157d67c6f0c0004', '8a8c32c257d67b2a0157d67b30380002');
COMMIT;
-- ----------------------------
-- Table structure for `student`
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
`pid` varchar(32) NOT NULL,
`student_name` varchar(64) DEFAULT NULL,
PRIMARY KEY (`pid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of `student`
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES ('8a8c32c257d67b2a0157d67bbc5c0003', 'Student1'), ('8a8c32c257d67b2a0157d67c6f0c0004', 'Student2');
COMMIT;代码下载
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