hibernate 双向多对多 注解

其实它的和 一对多 差不多，但是按照网上写法出现了一个问题，使得 双向的关系变成了单向的。

Person类

package cn.lzg;import java.util.ArrayList;import java.util.List;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.SequenceGenerator;import javax.persistence.Table;@Entity@Table(name = "person_lzg")public class Person {@Id@SequenceGenerator(name = "person_lzg", sequenceName = "p_seq", allocationSize = 1)@GeneratedValue(generator = "person_lzg", strategy = GenerationType.SEQUENCE)private Long p_id;@Column(name = "name")private String name;@ManyToMany(targetEntity = cn.lzg.Book.class, fetch = FetchType.LAZY)@JoinTable(name = "lzgp_lzgb", joinColumns = { @JoinColumn(name = "p_id") }, inverseJoinColumns = { @JoinColumn(name = "b_id") })// name中间表的名字,第一个自己的主键，第二个关联的主键private List<Book> books = new ArrayList<Book>();public Long getP_id() {return p_id;}public void setP_id(Long p_id) {this.p_id = p_id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public List<Book> getBooks() {return books;}public void setBooks(List<Book> books) {this.books = books;}}

Book类

package cn.lzg;import java.util.ArrayList;import java.util.List;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.SequenceGenerator;import javax.persistence.Table;@Entity@Table(name = "book_lzg")public class Book {@Id@SequenceGenerator(name = "book_lzg", sequenceName = "b_seq", allocationSize = 1)@GeneratedValue(generator = "book_lzg", strategy = GenerationType.SEQUENCE)private Long b_id;@Column(name = "name")private String name;@ManyToMany(targetEntity = cn.lzg.Person.class, fetch = FetchType.LAZY)<span style="color:#FF0000;">// 如果在上面使用mappedBy后,就成单向的了.也就是mappedBy出现的位置所在的类,这个类是被维护端,它只能被别人级联,不能去保存别人.// 这个问题搞了好久才发现，开始一直是单向的.</span>@JoinTable(name = "lzgp_lzgb", joinColumns = { @JoinColumn(name = "b_id") }, inverseJoinColumns = { @JoinColumn(name = "p_id") })private List<Person> persons = new ArrayList<Person>();public Long getB_id() {return b_id;}public void setB_id(Long b_id) {this.b_id = b_id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public List<Person> getPersons() {return persons;}public void setPersons(List<Person> persons) {this.persons = persons;}}

注意

<span style="color:#FF0000;">如果在上面ManyToMany注解中使用mappedBy,就成单向的了.因为mappedBy出现的位置所在的类,这个类是被维护端,它只能被别人级联,不能去保存别人<span style="color:#330033;">测试类</span></span><pre name="code" class="java">package cn.lzg;import java.util.ArrayList;import java.util.Date;import java.util.List;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.hibernate.service.ServiceRegistryBuilder;import org.junit.Test;public class TestHibernate {private static Configuration configuration = null;private static SessionFactory sessionFactory = null;private static ServiceRegistry serviceRegistry = null;private static Session session = null;static {/** * hibernate 4 貌失要这样获得sessionFactory 以前的configuration.buildSessionFactory();方法 过时了 */configuration = new Configuration().configure();serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()).buildServiceRegistry();sessionFactory = configuration.buildSessionFactory(serviceRegistry);session = sessionFactory.openSession();}@Test// 测试manytomanypublic void testM2M() {Person p1 = new Person();p1.setName("张三");Person p2 = new Person();p2.setName("李四");Person p3 = new Person();p3.setName("王五");List<Person> persons = new ArrayList<Person>();persons.add(p1);persons.add(p2);persons.add(p3);Book b1 = new Book();b1.setName("书本1");Book b2 = new Book();b2.setName("书本2");Book b3 = new Book();b3.setName("书本3");List<Book> books = new ArrayList<Book>();books.add(b1);books.add(b2);books.add(b3);p1.setBooks(books);b3.setPersons(persons);Transaction tx = session.beginTransaction();session.save(p1);session.save(p2);session.save(p3);session.save(b1);session.save(b2);session.save(b3);tx.commit();session.close();}}

结果生成了中间表

lzgp_lzgb 里面的关系p1 有三本书， p1,p2,p3都有b3