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hibernate入门使用系列 3-- xml关系映射篇（中）

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  • RyanPoy
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  • 来自: 长沙
   发表时间：2008-05-07   最后修改：2008-11-12

接上篇 hibernate入门使用系列 2-- xml关系映射篇（上）

上篇讲了1：1，那么这次继续讲1：n和n：1。

这次用到的例子是Father和child之间的关系。一个father可以有n个child，但是1个child只有一个father。这里只说生父。至于其他的继父、养父、干爹等等，不再范围之内。

好吧。还是同前面的一样。现建立实体模型如下：

 

 

根据模型创建数据库。sql脚本如下：

use HibernateQuickUse;
drop table if exists Child;
drop table if exists Father;

create table Father (
	id varchar(32) primary key,
	name varchar(32) not null
);

create table Child (
	id varchar(32) primary key,
	name varchar(128) not null,
	father_id varchar(32) not null,
	foreign key(father_id) references Father(id)
);

 

根据模型创建java对象。

Father.java：

package org.py.hib.relation.one2many;

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

/**
 * Father entity.
 */

@SuppressWarnings("serial")
public class Father implements java.io.Serializable
{
	private String id;

	private String name;

	private Set<Child> children = new HashSet<Child>(0);

	public Father()
	{
	}

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

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

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

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

	public Set<Child> getChildren()
	{
		return children;
	}

	public void setChildren(Set<Child> children)
	{
		this.children = children;
	}
}

 

 Child.java：

package org.py.hib.relation.one2many;

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

@SuppressWarnings("serial")
public class Child implements java.io.Serializable
{
	private String id;

	private String name;

	private Father father;

	public Child()
	{
	}

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

	public void setId(String 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;
	}

}

 

映射文件如下：

Father.hbm.xml：

<?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">

<hibernate-mapping>
    <class name="org.py.hib.relation.one2many.Father" table="father">
        <id name="id" type="java.lang.String" column="id" length="32">
            <generator class="uuid" />
        </id>

        <property name="name" type="java.lang.String" column="name" length="32" not-null="true"/>
        
	<set name="children" table="child" cascade="all" inverse="true">
            <key column="father_id" />
            <one-to-many class="org.py.hib.relation.one2many.Child" />
        </set>
    </class>
</hibernate-mapping>

这里要说说 "set" 这个标签里面的内容。

"name"是Father里面的属性的名字。

"table"表示它对应的是数据库中的哪个表。

cascade="all" 表示所有的操作都级联操作。

"inverse"表示关系的维护由谁来执行。true表示不由自己执行，而有对应的另外一方执行。false则相反，表示由自己维护关系。这里设置成 true 是由原因的。如果说把它设置成为false，那么就由他来维护关系了。

这里得说一下inverse属性的问题。在one-to-many中，如果关系由one来维护，那么会很麻烦，性能也会很低。每次对many一方的一条记录进行增、删、改 时都会多一次update操作。原因很简单，因为关系的维护设置在了one这一方，所以对many的每一次操作，one这一方都要维护一次双方的关系。

这个就好像皇帝和老百姓的关系。试问，是来一个老百姓，皇帝就宣布他是我的子民，还是由老百姓直接选择做那个皇帝的子民更加有效率呢？呵呵。不知道这个例子大家有没有明白。关于inverse的更具体的说明，在javaeye上搜一下，就会发现有很多。这里推荐一篇，我认为讲得很明白的：主题：inverse。

"key" 中的 "column" 表示在table(这里的table是child)中, 跟Father关联的字段名称。这里是"father_id"。可以看看开始的sql脚本。

one-to-many 表示father和children的关系。class则表示是同哪个类是这种关系。

 

 Child.hbm.xml：

<?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">

<hibernate-mapping>
    <class name="org.py.hib.relation.one2many.Child" table="child">
        <id name="id" type="java.lang.String" column="id" length="32" >
            <generator class="uuid" />
        </id>
        <property name="name" type="java.lang.String" column="name" length="128" not-null="true"/>

        <many-to-one name="father" class="org.py.hib.relation.one2many.Father" column="father_id" />
    </class>
</hibernate-mapping>

 这个里面主要就是多了一个many-to-one，表示child 和 father 的关系是"many-to-one"

 

测试代码如下：

One2ManyTest.java

package org.py.hib.relation.one2many;

import java.util.Set;

import junit.framework.Assert;
import junit.framework.TestCase;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.After;
import org.junit.Before;

public class One2ManyTest extends TestCase
{
	private SessionFactory factory;

	private static final String[] childname = new String[] { "child_1", "child_2", "child_3" };

	private static final String[] newchildname = new String[] { "new_child_1", "new_child_2", "new_child_3" };

	@Before
	public void setUp() throws Exception
	{
		Configuration conf = new Configuration().configure();
		factory = conf.buildSessionFactory();
	}

	/**
	 * 测试添加
	 * @throws Exception
	 */
	public void testSave() throws Exception
	{
		System.out.println("\n=== test save ===");

		Father father = new Father();
		father.setName("Father_1");

		Child child1 = new Child();
		child1.setName(childname[0]);

		Child child2 = new Child();
		child2.setName(childname[1]);

		Child child3 = new Child();
		child3.setName(childname[2]);

		father.getChildren().add(child1);
		father.getChildren().add(child2);
		father.getChildren().add(child3);

		child1.setFather(father);
		child2.setFather(father);
		child3.setFather(father);

		Session session = null;
		Transaction tran = null;
		try
		{
			session = factory.openSession();
			tran = session.beginTransaction();
			session.save(father);

			tran.commit();

			Assert.assertNotNull(father.getId());

			Assert.assertNotNull(child1.getId());
			Assert.assertNotNull(child2.getId());
			Assert.assertNotNull(child3.getId());

		} catch (Exception ex)
		{
			tran.rollback();
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}
	}

	private boolean isChildrenName(String name)
	{
		for (String n : childname)
		{
			if (n.equals(name))
				return true;
		}

		return false;
	}

	private boolean isNewChildrenName(String name)
	{
		for (String n : newchildname)
		{
			if (n.equals(name))
				return true;
		}

		return false;
	}

	/**
	 * 测试查询
	 * @throws Exception
	 */
	public void testFind() throws Exception
	{
		System.out.println("\n=== test find ===");
		Session session = null;
		try
		{
			session = factory.openSession();
			Father father = (Father) session.createQuery("from Father").list().get(0);

			Assert.assertNotNull(father.getId());
			Assert.assertEquals("Father_1", father.getName());

			Set<Child> children = father.getChildren();
			for (Child child : children)
			{
				Assert.assertEquals(child.getFather(), father);

				Assert.assertNotNull(child.getId());

				Assert.assertTrue(isChildrenName(child.getName()));
			}
		} catch (Exception ex)
		{
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}
	}

	/**
	 * 测试修改
	 * @throws Exception
	 */
	public void testModify() throws Exception
	{
		System.out.println("\n=== test modify ===");
		Session session = null;
		Transaction tran = null;
		try
		{
			session = factory.openSession();
			tran = session.beginTransaction();

			Father father = (Father) session.createQuery("from Father").list().get(0);
			father.setName("Father_2"); // 修改用户名 = m_name2.（原来用户名= m_name）

			Set<Child> children = father.getChildren();
			int i = 0;
			for (Child child : children)
			{
				child.setName(newchildname[i++]);
			}

			tran.commit();

		} catch (Exception ex)
		{
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}

		/*
		 * 修改后再查询
		 */
		System.out.println("\n=== test find after modify ===");
		try
		{
			session = factory.openSession();
			Father father = (Father) session.createQuery("from Father").list().get(0);

			Assert.assertNotNull(father.getId());
			Assert.assertEquals("Father_2", father.getName());

			Set<Child> children = father.getChildren();

			for (Child child : children)
			{
				Assert.assertEquals(child.getFather(), father);

				Assert.assertNotNull(child.getId());

				Assert.assertTrue(isNewChildrenName(child.getName()));
			}

		} catch (Exception ex)
		{
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}
	}

	/**
	 * 测试删除
	 * @throws Exception
	 */
	public void testDelete() throws Exception
	{
		System.out.println("\n=== test delete ===");
		Session session = null;
		Transaction tran = null;
		try
		{
			session = factory.openSession();
			tran = session.beginTransaction();

			Father father = (Father) session.createQuery("from Father").list().get(0);
			session.delete(father);
			tran.commit();

		} catch (Exception ex)
		{
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}

		/*
		 * 删除后再查询
		 */
		System.out.println("\n=== test find after delete ===");
		try
		{
			session = factory.openSession();

			Integer num = (Integer) session.createQuery("from Father").list().size();
			Assert.assertEquals(0, num.intValue());

			num = (Integer) session.createQuery("from Child").list().size();
			Assert.assertEquals(0, num.intValue());

		} catch (Exception ex)
		{
			throw ex;
		} finally
		{
			if (session != null)
			{
				try
				{
					session.close();
				} catch (Exception ex)
				{
					// nothing to do
				} finally
				{
					if (session != null)
						session = null;
				}
			}
		}
	}

	/**
	 * 
	 */
	@After
	public void tearDown() throws Exception
	{
		factory.close();
	}

}
 

这里不得不再重申以下 one-to-many 中 inverse 关系的维护问题。 在one-to-many中，把inverse放到many中来维护是一个好的习惯。大家可以把上面的inverse改成false，看看会发生什么情况。

在inverse=true的时候，输出结果如下：

=== test save ===
Hibernate: insert into father (name, id) values (?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)

=== test find ===
Hibernate: select father0_.id as id13_, father0_.name as name13_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id14_0_, children0_.name as name14_0_, children0_.father_id as father3_14_0_ from child children0_ where children0_.father_id=?

=== test modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?
Hibernate: update father set name=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?

=== test find after modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?

=== test delete ===
Hibernate: select father0_.id as id33_, father0_.name as name33_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id34_0_, children0_.name as name34_0_, children0_.father_id as father3_34_0_ from child children0_ where children0_.father_id=?
Hibernate: delete from child where id=?
Hibernate: delete from child where id=?
Hibernate: delete from child where id=?
Hibernate: delete from father where id=?

=== test find after delete ===
Hibernate: select father0_.id as id33_, father0_.name as name33_ from father father0_
Hibernate: select child0_.id as id34_, child0_.name as name34_, child0_.father_id as father3_34_ from child child0_
 

而改成 inverse=false后，testDelete()是没法通过的。输出如下：

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.

=== test save ===
Hibernate: insert into father (name, id) values (?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: update child set father_id=? where id=?
Hibernate: update child set father_id=? where id=?
Hibernate: update child set father_id=? where id=?

=== test find ===
Hibernate: select father0_.id as id13_, father0_.name as name13_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id14_0_, children0_.name as name14_0_, children0_.father_id as father3_14_0_ from child children0_ where children0_.father_id=?

=== test modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?
Hibernate: update father set name=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?

=== test find after modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?

=== test delete ===
Hibernate: select father0_.id as id33_, father0_.name as name33_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id34_0_, children0_.name as name34_0_, children0_.father_id as father3_34_0_ from child children0_ where children0_.father_id=?
Hibernate: update child set father_id=null where father_id=?

 错误信息如下：

具体的出错原因是：违反了非空约束。

得修改sql脚本，把Child的建表脚本中的：

                     father_id varchar(32) not null, 修改成为：father_id varchar(32),

才能通过。这个时候输出的结果是：

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.

=== test save ===
Hibernate: insert into father (name, id) values (?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: insert into child (name, father_id, id) values (?, ?, ?)
Hibernate: update child set father_id=? where id=?
Hibernate: update child set father_id=? where id=?
Hibernate: update child set father_id=? where id=?

=== test find ===
Hibernate: select father0_.id as id13_, father0_.name as name13_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id14_0_, children0_.name as name14_0_, children0_.father_id as father3_14_0_ from child children0_ where children0_.father_id=?

=== test modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?
Hibernate: update father set name=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?
Hibernate: update child set name=?, father_id=? where id=?

=== test find after modify ===
Hibernate: select father0_.id as id23_, father0_.name as name23_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id24_0_, children0_.name as name24_0_, children0_.father_id as father3_24_0_ from child children0_ where children0_.father_id=?

=== test delete ===
Hibernate: select father0_.id as id33_, father0_.name as name33_ from father father0_
Hibernate: select children0_.father_id as father3_1_, children0_.id as id1_, children0_.id as id34_0_, children0_.name as name34_0_, children0_.father_id as father3_34_0_ from child children0_ where children0_.father_id=?
Hibernate: update child set father_id=null where father_id=?
Hibernate: delete from child where id=?
Hibernate: delete from child where id=?
Hibernate: delete from child where id=?
Hibernate: delete from father where id=?

=== test find after delete ===
Hibernate: select father0_.id as id33_, father0_.name as name33_ from father father0_
Hibernate: select child0_.id as id34_, child0_.name as name34_, child0_.father_id as father3_34_ from child child0_
 

所以，inverse的设置是很重要的一个事情。

附件中包含了源代码。这里说明一下。源代码中没有包含数据库驱动的jar包和hibernate3.1的jar包。需要大家自己添加。

 

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  • hantsy
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  • 文章: 672
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  • 来自: 广州
   发表时间：2008-05-10  

在这种one to many 的双向关联中，按照需求，更符合Hibernate的作法是还要在你的 Child 映射文件的关联中加上not-null="true"的约束。

如果是单向的one to many 关联（没有Child 到Parent 的关联），这个约束可以加在Parent的映射文件的set定义中去。
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  • e3002
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   发表时间：2008-05-27  
你好。最近遇到个问题。也是一对多双向关联的问题，举例
一个题目可以有a。b。c。d四个选项。题目类：subject 选项类 chooseItem
用户第一次建立题目是 可能是这样、
那个省人口最多
A.河南
B.河北
C.湖北
D.湖南
ok。保存入库，但用户下次修改时
可能如下
那个省人口最多
A.河南
B.河北
注意：只剩下两个选项 到此，此时的操作应该包括删除和修改多方的操作，这个hibernate能自动处理吗？该怎么处理？请赐教

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  • wm920
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   发表时间：2008-06-16  
请问下 ···

我要是实现自定义表的字段···怎么实现咯 ··
他们的数据能进行查进去 么 ，因为表的关联是一下子取（通SET与GET）全部的数据···  会报SQL语句的异常···
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  • RyanPoy
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   发表时间：2008-06-17  
e3002 写道
你好。最近遇到个问题。也是一对多双向关联的问题，举例
一个题目可以有a。b。c。d四个选项。题目类：subject 选项类 chooseItem
用户第一次建立题目是 可能是这样、
那个省人口最多
A.河南
B.河北
C.湖北
D.湖南
ok。保存入库，但用户下次修改时
可能如下
那个省人口最多
A.河南
B.河北
注意：只剩下两个选项 到此，此时的操作应该包括删除和修改多方的操作，这个hibernate能自动处理吗？该怎么处理？请赐教



完全可以。看帖子里面的测试代码。里面有完整的增删该查。你可以仿照从而写出你的业务逻辑。
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  • RyanPoy
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wm920 写道

我要是实现自定义表的字段···怎么实现咯 ··


不明白什么叫自定义表的字段。能否举一例？

wm920 写道

他们的数据能进行查进去 么 ，因为表的关联是一下子取（通SET与GET）全部的数据···  会报SQL语句的异常

表的关联可以不一下子全取。hibernate提供了 延迟处理。3版本后默认为lazy。

关于lazy的用法参看这个，http://www.hibernate.org/162.html

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  • LuckyAngel
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   发表时间：2008-10-24  
Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList
我的程序中出现这个错误,是什么意思?请教一下
我用的是一对多关系映射,一的这方用的是List集合
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  • rmn190
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一个问题:
   现在你例子中是双向关联, 也就是说child类有对father类的引向, 这样在Child.hbm.xml中就有了<many-to-one name="father" class="org.py.hib.relation.one2many.Father" column="father_id" />, 这里的inverse是默认为false的. 这时两表间的引用由child类的setFather触发.

  若业务要求为单向关联,也就是说在child这边不再有father的引用, 这样一来两表间的关联关系只能由father类来维护了, 当然在<set name="children" table="child" cascade="all" >里的inverse默认为false的, 可这样做效率上是受影响的:  当加child集合时hibernate得去检查看哪个child与father的关系有改变, 而假若由child这边来维护的话,就不会有这样效率方面的问题.

  可在child的配置里若没有对father的引用后,我们也就无从下手了,不能两全其美.
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  • 流浪者A
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   发表时间：2008-11-05  
这个例子经常见到，很容易理解，很好的例子~·
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  • xiaojiit
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   发表时间：2008-12-04  
能不能写一个用DetachedCriteria进行查询的例子呢？谢谢了！
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