hibernate多对多关系
2024-08-29 07:18:03
package com.manytomany; import java.util.HashSet;
import java.util.Set; public class Student {
private Long id;
private String name; private Set<Teacher> teachers = new HashSet<Teacher>(); // 关联的老师们 public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public Set<Teacher> getTeachers() {
return teachers;
} public void setTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
} @Override
public String toString() {
return "[Student: id=" + id + ", name=" + name + "]";
}
}
package com.manytomany; import java.util.HashSet;
import java.util.Set; public class Teacher {
private Long id;
private String name; private Set<Student> students = new HashSet<Student>(); // 关联的学生们 public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public Set<Student> getStudents() {
return students;
} public void setStudents(Set<Student> students) {
this.students = students;
} @Override
public String toString() {
return "[Teacher: id=" + id + ", name=" + name + "]";
}
}
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.manytomany">
<class name="Student" table="t_student">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name" /> <!--
teachers属性，Set集合，表达的是本类与Teacher的多对多的关系
table属性：中间表（集合表）
key子元素：集合外键（引用当前表主键的那个外键）
-->
<set name="teachers" table="teacher_student" inverse="false">
<key column="studentId"></key>
<many-to-many class="Teacher" column="teacherId"></many-to-many>
</set>
</class>
</hibernate-mapping>
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.manytomany">
<class name="Teacher" table="teacher">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name" type="string" column="name" /> <!-- students属性，Set集合，表达的是本类与Student的多对多的关系 -->
<set name="students" table="teacher_student" inverse="true">
<key column="teacherId"></key>
<many-to-many class="Student" column="studentId"></many-to-many>
</set>
</class>
</hibernate-mapping>
package com.manytomany.test; import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.EnumSet; import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.Test; import com.hello.Account;
import com.hello.User;
import com.manytomany.Student;
import com.manytomany.Teacher; public class HelloTest { private static SessionFactory sessionFactory; static {
sessionFactory = new Configuration()
.configure() // 读取配置文件
.buildSessionFactory();
} // 根据配置生成表结构
@Test
public void test() {
//hibernate 5.0
Configuration conf = new Configuration().configure();//1、读取配置文件
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().configure().build();
Metadata metadata = new MetadataSources(serviceRegistry).buildMetadata();
} @Test
public void hello(){ Session session=sessionFactory.openSession();
Transaction tx = session.beginTransaction();
//==================================================
Student student1 = new Student();
student1.setName("王同学"); Student student2 = new Student();
student2.setName("李同学"); Teacher teacher1 = new Teacher();
teacher1.setName("赵老师"); Teacher teacher2 = new Teacher();
teacher2.setName("蔡老师"); // 关联起来
student1.getTeachers().add(teacher1);
student1.getTeachers().add(teacher2);
student2.getTeachers().add(teacher1);
student2.getTeachers().add(teacher2); teacher1.getStudents().add(student1);
teacher1.getStudents().add(student2);
teacher2.getStudents().add(student1);
teacher2.getStudents().add(student2); // 保存
session.save(student1);
session.save(student2);
session.save(teacher1);
session.save(teacher2); //==================================================
tx.commit();
} // 解除关联关系
@Test
public void testRemoveRelation() {
Session session = sessionFactory.openSession();
session.beginTransaction();
// ------------------------------------------- // 如果inverse=false就可以解除，如果为true就不可以解除（删除中间表中的记录）
// Teacher teacher = (Teacher) session.get(Teacher.class, 3L);
// teacher.getStudents().clear();
Student student=session.get(Student.class, 4l);
student.getTeachers().clear(); // -------------------------------------------
session.getTransaction().commit();
session.close();
}
// 删除对象，对关联对象的影响
@Test
public void testDelete() {
Session session = sessionFactory.openSession();
session.beginTransaction();
// ------------------------------------------- // 删除老师方
// a，如果没有关联的对方：能删除
// b，如果有关联的对方且inverse=false，由于可以维护关联关系，它就会先删除关联关系，再删除自己。
// c，如果有关联的对方且inverse=true，由于不能维护关联关系，所以会直接执行删除自己，就会有异常
// Teacher teacher = (Teacher) session.get(Teacher.class, 5L);
// session.delete(teacher);
Student student=session.get(Student.class, 6l);
session.delete(student);
// -------------------------------------------
session.getTransaction().commit();
session.close();
} @Test
public void testGet(){ Session session=sessionFactory.openSession(); }
}
删除打印sql语句
Hibernate:
select
student0_.id as id1_1_0_,
student0_.name as name2_1_0_
from
t_student student0_
where
student0_.id=?
Hibernate:
delete
from
teacher_student
where
studentId=?
Hibernate:
delete
from
t_student
where
id=?
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