Hibernate----@Annotation----一对多----级联-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_11034/article/details/81921708

本文详细介绍了如何在Hibernate中实现一对多和多对一关系，包括实体类的设计、属性注解的使用以及级联操作的实践。

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一对多,双向,"一"的一方

package com.pegasus.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;

//在实体类的类名前
//标注是实体
//对应的表名
//相当于xml的
//<class name="com.pegasus.domain.Group" table="t_group"></class>
@Entity
@Table(name="t_group")
public class Group {
	private int id;
	private String name;
	private Set<User> users = new HashSet<User>();

	//在主键的get方法前
	//标注主键,以及生成主键策略
	//相当于<id name="id"><generator class="native"></generator></id>
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}

	//在一般属性的get方法前
	//一般的列名前不需要标注
	//相当于<property name="name"></property>
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

	//在一对多"一"的一方关联的集合前
	//使用@OneToMany标注,并标明"mappedBy",即关联的"多"的一方所对应的类的属性
	//cascade参数标明级联的方式,如果不需要级联可以省略
	//相当于<set name="users">
	//             <key column="groupId"></key>
	//             <one-to-many class="com.pegasus.domain.User"/>
        //         </set>
	@OneToMany(mappedBy="group",
		cascade={CascadeType.ALL}
		)
	
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
}

一对多,双向,"多"的一方

package com.pegasus.domain;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
//在实体类的类名前
//标注是实体
//对应的表名
//相当于xml的
//<class name="com.pegasus.domain.User" table="t_user"></class>
@Entity
@Table(name="t_user")
public class User {
	private int id;
	private String name;
	private Group group;
	
	//在主键的get方法前
	//标注主键,以及生成主键策略
	//相当于<id name="id"><generator class="native"></generator></id>
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	
	//在一般属性的get方法前
	//一般的列名前不需要标注
	//相当于<property name="name"></property>
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	//在一对多"多"的一方关联的属性get方法前
	//使用@ManyToOne标注
	//cascade参数标明级联的方式,如果不需要级联可以省略
	//相当于<many-to-one name="group" column="groupId"></many-to-one>
	@ManyToOne(cascade={CascadeType.ALL})
	public Group getGroup() {
		return group;
	}
	public void setGroup(Group group) {
		this.group = group;
	}
}

单元测试类

package com.pegasus.domain;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class HibernateORMappingTest {
	private static SessionFactory sessionFactory;
	
	@BeforeClass
	public static void beforeClass() {
		new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
		sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
	}
	@AfterClass
	public static void afterClass() {
		sessionFactory.close();
	}
	/**级联保存*/
	@Test
	public void testSaveUser() {
		System.out.print("begin to testSaveUser()");
		User u = new User();
		u.setName("u1");
		Group g = new Group();
		g.setName("g1");
		u.setGroup(g);
		Session s = sessionFactory.getCurrentSession();
		s.beginTransaction();
		//s.save(g);
		s.save(u);
		s.getTransaction().commit();
	}
	
//	@Test
//	public void testSaveGroup() {
//		System.out.print("begin to testSaveGroup()");
//		User u1 = new User();
//		u1.setName("u1");
//		User u2 = new User();
//		u2.setName("u2");
//		Group g = new Group();
//		g.setName("g1");
//		g.getUsers().add(u1);
//		g.getUsers().add(u2);
//		u1.setGroup(g);
//		u2.setGroup(g);
//		Session s = sessionFactory.getCurrentSession();
//		s.beginTransaction();
//		s.save(g);
//		s.getTransaction().commit();
//	}
	/**级联查询*/
	@Test
	public void testGetUser() {
		System.out.print("begin to testGetUser()");
//		testSaveGroup();
		
		Session s = sessionFactory.getCurrentSession();
		s.beginTransaction();
		User u = (User)s.get(User.class, 1);
		
		s.getTransaction().commit();
		System.out.println(u.getGroup().getName());
	}
	
//	@Test
//	public void testDeleteUser() {
//		System.out.print("begin to testDeleteUser()");	
//		testSaveGroup();
//		
//		Session s = sessionFactory.getCurrentSession();
//		s.beginTransaction();
//		//User u = (User)s.load(User.class, 1);
//		//u.setGroup(null);
//		//s.delete(u);
//		s.createQuery("delete from User u where u.id = 1").executeUpdate();
//		s.getTransaction().commit();
//		
//	}

	/**级联修改*/
	@Test
	public void testUpdateUser() {
		System.out.print("begin to testUpdateUser()");	
//		testSaveGroup();
		
		Session s = sessionFactory.getCurrentSession();
		s.beginTransaction();
		User u = (User)s.get(User.class, 1);
		
		s.getTransaction().commit();
		
		u.setName("user");
		u.getGroup().setName("group");
		
		Session s2 = sessionFactory.getCurrentSession();
		s2.beginTransaction();
		s2.update(u);
		
		s2.getTransaction().commit();
	}
	
	/**级联删除*/
	@Test
	public void testDeleteGroup() {
		System.out.print("begin to testDeleteGroup()");	
		testSaveGroup();
		
		Session s = sessionFactory.getCurrentSession();
		s.beginTransaction();
		//User u = (User)s.load(User.class, 1);
		//u.setGroup(null);
		//s.delete(u);
		Group g = (Group)s.load(Group.class, 1);
		s.delete(g);
		//s.createQuery("delete from User u where u.id = 1").executeUpdate();
		s.getTransaction().commit();
		
	}	
	
	
//	@Test
//	public void testSchemaExport() {
//		new SchemaExport(new AnnotationConfiguration().configure()).create(true, true);
//	}
	
//	public static void main(String[] args) {
//		beforeClass();
//	}
}

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/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/hibtest</property>
        <property name="connection.username">root</property>
        <property name="connection.password">123</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
       
        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>
        <!-- <property name="format_sql">true</property> -->

        <!-- Drop and re-create the database schema on startup
        <property name="hbm2ddl.auto">update</property>
		 -->
        <!--  
        
		<mapping resource="com/pegasus/domain/Group.hbm.xml"/>
		 <mapping resource="com/pegasus/domain/User.hbm.xml"/>
		 -->
		 <mapping class="com.pegasus.domain.Group"/>
		<mapping class="com.pegasus.domain.User"/>
		
    </session-factory>

</hibernate-configuration>