hibernate--关联关系的CRUD
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多对一单向关联：
Group.java:
package com.bean;import java.util.HashSet;import java.util.Set;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="t_group")public class Group {private int id;private String name;@Id@GeneratedValuepublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}
User.java:
package com.bean;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.OneToMany;import javax.persistence.Table;import org.hibernate.annotations.Cascade;@Entity@Table(name="t_user")public class User {private int id;private String name;private Group group;@ManyToOne(cascade={CascadeType.ALL}) //cascade---级联操作public Group getGroup() {return group;}public void setGroup(Group group) {this.group = group;}@Id@GeneratedValuepublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}
hibernate.cfg.xml:
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory><property name="connection.driver_class">com.mysql.jdbc.Driver</property><property name="connection.url">jdbc:mysql://localhost:3306/user</property><property name="connection.username">root</property><property name="connection.password">root</property><property name="dialect">org.hibernate.dialect.MySQLDialect</property><property name="show_sql">true</property><property name="hbm2ddl.auto">update</property><property name="show_sql">true</property><property name="format_sql">true</property><property name="current_session_context_class">thread</property><mapping class="com.bean.Group"/><mapping class="com.bean.User"/><!-- <mapping resource="com/bean/User.hbm.xml"/><mapping resource="com/bean/Group.hbm.xml"/>--></session-factory></hibernate-configuration>
测试：
package com.test;import org.hibernate.Query;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.AnnotationConfiguration;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistryBuilder;import org.hibernate.tool.hbm2ddl.SchemaExport;import com.bean.Group;import com.bean.User;import com.bean.User2;public class Test_W_H {public static void main(String []args) {Configuration cfg = new Configuration();cfg.configure(); //加载hibernate配置文件SessionFactory sessionFactory = cfg.buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties()).buildServiceRegistry());Session session = sessionFactory.getCurrentSession();session.beginTransaction(); //开启事务User user = new User();user.setName("代里");Group group = new Group();group.setName("team1");user.setGroup(group);session.save(user);session.getTransaction().commit(); // 事务提交System.out.println("the end");}}
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一对多双向关联：
在Group.java增加属性：
private Set<User> users = new HashSet<User>();@OneToMany(mappedBy="group",cascade={CascadeType.ALL})public Set<User> getUsers() {return users;}public void setUsers(Set<User> users) {this.users = users;}
测试：
session.beginTransaction(); //开启事务User user1 = new User();user1.setName("代里");User user2 = new User();user2.setName("张三");Group group = new Group();group.setName("team1");group.getUsers().add(user1);group.getUsers().add(user2);user1.setGroup(group);user2.setGroup(group);session.save(group);session.getTransaction().commit(); // 事务提交
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read读取：
OneToMany:需要配置fetch：(fetch默认状态为lazy)
@OneToMany(mappedBy="group",cascade={CascadeType.ALL},fetch=FetchType.EAGER)
ManyToOne则不需要配置，因为fetch默认状态为eager
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级联删除（防止级联删除效应）：
1、取消级联关系
User user = (User)session.get(User.class, 7);user.setGroup(null);session.delete(user);session.getTransaction().commit(); // 事务提交
2、设置Hql来控制。
session.createQuery("delete from User u where u.id = 8").executeUpdate();
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红太狼
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朱雀
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