步骤1.新建java项目:JPAManyToMany,将hibernate包以及mysql驱动包导入
步骤2.在类路径下新建xml文件persistence.xml,将其放入META-INF文件夹下,其代码如下:
<?xml version="1.0" encoding="UTF-8"?> <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="itcast" transaction-type="RESOURCE_LOCAL"> <properties> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/itcast?useUnicode=true&characterEncoding=UTF-8" /> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/> <property name="hibernate.connection.driver_class" value="org.gjt.mm.mysql.Driver" /> <property name="hibernate.connection.username" value="root" /> <property name="hibernate.connection.password" value="root" /> <property name="hibernate.max_fetch_depth" value="3" /> <property name="hibernate.hbm2ddl.auto" value="update" /> </properties> </persistence-unit> </persistence>
步骤3.编写实体Bean类
Student代码如下:
package cn.itcast.bean; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; @Entity public class Student { private Integer id; private String name; private Set<Teacher> teachers = new HashSet<Teacher>(); public Student(){} public Student(String name) { this.name = name; } /** *Student为关系的维护端,有对外键增删改查的权利 *在关系的维护端创建关系表为student_teacher,并指定了关系被维护端的外键为teacher_id, *关系维护端的外键为student_id * @JoinTable(name="student_teacher",inverseJoinColumns=@JoinColumn(name="teacher_id") * ,joinColumns=@JoinColumn(name="student_id")) */ @ManyToMany(cascade=CascadeType.REFRESH) @JoinTable(name="student_teacher",inverseJoinColumns=@JoinColumn(name="teacher_id") ,joinColumns=@JoinColumn(name="student_id")) public Set<Teacher> getTeachers() { return teachers; } public void setTeachers(Set<Teacher> teachers) { this.teachers = teachers; } @Id @GeneratedValue public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @Column(length=10,nullable=false) public String getName() { return name; } public void setName(String name) { this.name = name; } /** * 增加teacher的方法 */ public void addTeacher(Teacher teacher){ this.teachers.add(teacher); } /** * 删除teacher的方法 */ public void removeTeacher(Teacher teacher){ /* * 判断该集合中是否包含该方法,包含就删除掉, * 要在Teacher.java中重载hashCode()和equals(Object obj)方法, * 作用是为了判断这个集合中的teacher是否与要删除的teacher对象相等,根据id判断 */ if(this.teachers.contains(teacher)) this.teachers.remove(teacher); } }
Teacher的代码如下:
package cn.itcast.bean; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.ManyToMany; @Entity public class Teacher { private Integer id; private String name; private Set<Student> students = new HashSet<Student>(); public Teacher(){} public Teacher(String name) { this.name = name; } /** * mappedBy="teachers" 说明Teacher为关系被维护端,没有对外键增删改查的权利 */ @ManyToMany(cascade=CascadeType.REFRESH,mappedBy="teachers") public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } @Id @GeneratedValue public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } @Column(length=10,nullable=false) public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public int hashCode() { final int PRIME = 31; int result = 1; result = PRIME * result + ((id == null) ? 0 : id.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; final Teacher other = (Teacher) obj; if (id == null) { if (other.id != null) return false; } else if (!id.equals(other.id)) return false; return true; } }
步骤4.创建junit测试
package junit.test; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import org.junit.BeforeClass; import org.junit.Test; import cn.itcast.bean.Student; import cn.itcast.bean.Teacher; public class ManyToManyTest { @BeforeClass public static void setUpBeforeClass() throws Exception { } //分别保存老师和学生 @Test public void save(){ EntityManagerFactory factory = Persistence.createEntityManagerFactory("itcast"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); em.persist(new Student("小学生")); em.persist(new Teacher("大老师")); em.getTransaction().commit(); em.close(); factory.close(); } //建立老师和学生的关系 @Test public void buildTS(){ EntityManagerFactory factory = Persistence.createEntityManagerFactory("itcast"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); Student student = em.getReference(Student.class, 1); student.addTeacher(em.getReference(Teacher.class, 1)); em.getTransaction().commit(); em.close(); factory.close(); } //解除老师和学生的关系 @Test public void removeTS(){ EntityManagerFactory factory = Persistence.createEntityManagerFactory("itcast"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); Student student = em.getReference(Student.class, 1); student.removeTeacher(em.getReference(Teacher.class, 1)); em.getTransaction().commit(); em.close(); factory.close(); } /** * 删除老师 * 在删除老师的时候,因为老师是关系被维护端 * 所以要首先解除老师跟学生的关系,然后才能删除老师 */ @Test public void deleteTeacher(){ EntityManagerFactory factory = Persistence.createEntityManagerFactory("itcast"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); Teacher teacher = em.getReference(Teacher.class, 1); Student student = em.getReference(Student.class, 1); student.removeTeacher(teacher); em.remove(teacher); em.getTransaction().commit(); em.close(); factory.close(); } /** * 删除学生 * 在删除学生的时候,因为学生是关系的维护端, * 这样会直接解除老师跟学生的关系,并且可以删除掉学生 */ @Test public void deleteStudent(){ EntityManagerFactory factory = Persistence.createEntityManagerFactory("itcast"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); Student student = em.getReference(Student.class, 1); em.remove(student); em.getTransaction().commit(); em.close(); factory.close(); } }
看能将表创建出来,并插入数据即可。