hibernate一对多单向关联关系

程序员文章站 2022-03-08 13:10:26

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前一段时间一直在忙于一个演示项目，近日完工了，就回过看来看了看hibernate，hibernate中一对多的关联最为常见，就简单的谈谈这个，言语不对，忘指点：

下面我以Father 和 Child为例为说明：

先来看看两个实体类

1）Father.java

package com.syp.pojo;

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

/**
 * Father entity.
 * 
 * @author MyEclipse Persistence Tools
 */

public class Father implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private Set childs = new HashSet(0);

	// Constructors

	/** default constructor */
	public Father() {
	}

	/** full constructor */
	public Father(String name, Set childs) {
		this.name = name;
		this.childs = childs;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Set getChilds() {
		return this.childs;
	}

	public void setChilds(Set childs) {
		this.childs = childs;
	}

}

对应的hbm.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
	Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
	<class name="com.syp.pojo.Father" table="father" catalog="test">
		<id name="id" type="java.lang.Integer">
			<column name="id" />
		</id>
		<property name="name" type="java.lang.String">
			<column name="name" length="30" />
		</property>
		<set name="childs" inverse="true" cascade="all">
			<key>
				<column name="father_id" />
			</key>
			<one-to-many class="com.syp.pojo.Child" />
		</set>
	</class>
</hibernate-mapping>

2）Child.java

package com.syp.pojo;

/**
 * Child entity.
 * 
 * @author MyEclipse Persistence Tools
 */

public class Child implements java.io.Serializable {

	// Fields

	private Integer id;
	private Father father;
	private String name;

	// Constructors

	/** default constructor */
	public Child() {
	}

	/** full constructor */
	public Child(Father father, String name) {
		this.father = father;
		this.name = name;
	}

	// Property accessors

	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public Father getFather() {
		return this.father;
	}

	public void setFather(Father father) {
		this.father = father;
	}

	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

}

对应的hbm.xml如下：

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.syp.pojo.Child" table="child" catalog="test">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
          
        </id>
        <many-to-one name="father" class="com.syp.pojo.Father" fetch="select">
            <column name="father_id" />
        </many-to-one>
        <property name="name" type="java.lang.String">
            <column name="name" length="30" />
        </property>
    </class>
</hibernate-mapping>

3）关于hibernate.cfg.xml的配置如下：

<?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">

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

	<session-factory>
		<property name="dialect">
			org.hibernate.dialect.MySQLDialect
		</property>
		<property name="connection.url">
			jdbc:mysql://localhost:3306/test
		</property>
		<property name="connection.username">root</property>
		<property name="connection.password">root</property>
		<property name="connection.driver_class">
			com.mysql.jdbc.Driver
		</property>
		<property name="myeclipse.connection.profile">
			mysqltest
		</property>
		
		<property name="show_sql">true</property>
		<mapping resource="com/syp/pojo/Father.hbm.xml" />
		<mapping resource="com/syp/pojo/Child.hbm.xml" />


	</session-factory>

</hibernate-configuration>

4） HibernateSessionFactory.java如下，小弟是用E直接生成的，对E不齿的就请原谅了

package com.syp.hib;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

/**
 * Configures and provides access to Hibernate sessions, tied to the current
 * thread of execution. Follows the Thread Local Session pattern, see
 * {@link http://hibernate.org/42.html }.
 */
public class HibernateSessionFactory {

	/**
	 * Location of hibernate.cfg.xml file. Location should be on the classpath
	 * as Hibernate uses #resourceAsStream style lookup for its configuration
	 * file. The default classpath location of the hibernate config file is in
	 * the default package. Use #setConfigFile() to update the location of the
	 * configuration file for the current session.
	 */
	private static String CONFIG_FILE_LOCATION = "/com/syp/hib/hibernate.cfg.xml";
	private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
	private static Configuration configuration = new Configuration();
	private static org.hibernate.SessionFactory sessionFactory;
	private static String configFile = CONFIG_FILE_LOCATION;

	static {
		try {
//			configuration.configure(configFile);
			 configuration.configure();
			sessionFactory = configuration.buildSessionFactory();
		} catch (Exception e) {
			System.err.println("%%%% Error Creating SessionFactory %%%%");
			e.printStackTrace();
		}
	}

	private HibernateSessionFactory() {
	}

	/**
	 * Returns the ThreadLocal Session instance. Lazy initialize the
	 * <code>SessionFactory</code> if needed.
	 * 
	 * @return Session
	 * @throws HibernateException
	 */
	public static Session getSession() throws HibernateException {
		Session session = (Session) threadLocal.get();

		if (session == null || !session.isOpen()) {
			if (sessionFactory == null) {
				rebuildSessionFactory();
			}
			session = (sessionFactory != null) ? sessionFactory.openSession()
					: null;
			threadLocal.set(session);
		}

		return session;
	}

	/**
	 * Rebuild hibernate session factory
	 * 
	 */
	public static void rebuildSessionFactory() {
		try {
			configuration.configure(configFile);
			// configuration.configure();
			sessionFactory = configuration.buildSessionFactory();
		} catch (Exception e) {
			System.err.println("%%%% Error Creating SessionFactory %%%%");
			e.printStackTrace();
		}
	}

	/**
	 * Close the single hibernate session instance.
	 * 
	 * @throws HibernateException
	 */
	public static void closeSession() throws HibernateException {
		Session session = (Session) threadLocal.get();
		threadLocal.set(null);

		if (session != null) {
			session.close();
		}
	}

	/**
	 * return session factory
	 * 
	 */
	public static org.hibernate.SessionFactory getSessionFactory() {
		return sessionFactory;
	}

	/**
	 * return session factory
	 * 
	 * session factory will be rebuilded in the next call
	 */
	public static void setConfigFile(String configFile) {
		HibernateSessionFactory.configFile = configFile;
		sessionFactory = null;
	}

	/**
	 * return hibernate configuration
	 * 
	 */
	public static Configuration getConfiguration() {
		return configuration;
	}

}

5）以下测试的类：Test.java

package com.syp.test;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;

import com.syp.hib.HibernateSessionFactory;
import com.syp.pojo.Child;
import com.syp.pojo.Father;

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Session session;
		Father f = new Father();
		f.setId(1);
		f.setName("likui");
		Child c = new Child();
		c.setName("c");
		c.setId(1);
		c.setFather(f);
		f.getChilds().add(c);

		session = HibernateSessionFactory.getSession();
		 session.beginTransaction();
		 session.save(f);
		 session.getTransaction().commit();

//		Father f2 = (Father) session.get(Father.class, 1);
//
//		System.out.println(f2.getName());
		Query query = session.createQuery("from Father");
		List l = query.list();
		for (int i = 0; i < l.size(); i++) {
			Father f3 = (Father) l.get(i);
			System.out.println(f3.getName());
		}

	}

}

在hibernate 中一对多关键点于对"inverse", "cascade"的设置，首先来说明一下这两个属性有什么作用，"inverse"的中文意思是：adj.
倒转的, 反转的
n.
反面
v.
倒转

是一个多属性的词，我想你已经明白了，它表示与此类关联的关系由谁来维护，通俗的讲就是，此类及与与此类关联的类，这两个类之间的关系由哪一方来维护。它的取值只有两个“true"or"false"，默认值为"false".

其次是"cascade",这个是一个很重要的属性，如果你想体会hibernate的强大，你一定要注意它了，因它它会给你带来意想不到的惊喜。

它的取值：

none：在保存，删除或修改当前对象时，不对其附属对象（关联对象）进行级联
hibernate一对多单向关联关系

博客分类：原创 HibernateMyeclipseXMLMySQLC#           操作。它是默认值。
    save-update：在保存，更新当前对象时，级联保存，更新附属对象(临时对象，
          游离对象)。
    delete：在删除当前对象时，级联删除附属对象。
hibernate一对多单向关联关系

博客分类：原创 HibernateMyeclipseXMLMySQLC#     all：所有情况下均进行级联操作，即包含save-update和delete操作。
    delete-orphan：删除和当前对象解除关系的附属对象。
，请各位注意一下Father.hbm.xml文件，为了便于说明，在贴出来

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
	Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
	<class name="com.syp.pojo.Father" table="father" catalog="test">
		<id name="id" type="java.lang.Integer">
			<column name="id" />
		</id>
		<property name="name" type="java.lang.String">
			<column name="name" length="30" />
		</property>
		<set name="childs" inverse="true" cascade="all">

                                    在这里设置了“inverse=true"，它表里当在操作Father与Child时，再者之间的关系由对方去管理，

就是由Chil来管理，“casCade=all",就是我们在对此对象进行有的操作时，与此关联的附属对象均会被级联操作，如果是保存的话，

附属对象也会被保存，其它操作也是如此。

			<key>
				<column name="father_id" />
			</key>
			<one-to-many class="com.syp.pojo.Child" />
		</set>
	</class>
</hibernate-mapping>

在测试的代码中我们看到只保存了Father ,没有保存Child，Child也会被保存，就是CasCade的作用。

在说到这，欢迎各位大牛指点。

源码可下载：

hibernateTest.rar (424.6 KB)
下载次数: 138

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