hibernate 1-1(具体解释)

版权声明：本文为博主原创文章，未经博主同意不得转载。 https://blog.csdn.net/qilixiang012/article/details/27870343

域模型


关系数据模型:

  • 依照外键映射:

  • 依照主键映射:


基于外键映射的 1-1
  • 对于基于外键的1-1关联。其外键能够存放在随意一边。在须要存放外键一端。添加many-to-one元素。为many-to-one元素添加unique=“true” 属性来表示为1-1关联

  • 还有一端须要使用one-to-one元素。该元素使用 property-ref 属性指定使用被关联实体主键以外的字段作为关联字段

－不使用 property-ref 属性的 sql

－使用 property-ref 属性的 sql


为什么不两边都使用外键映射的 1-1


这样就不是一对一关系映射了。


基于主键映射的 1-1

  • 基于主键的映射策略:指一端的主键生成器使用 foreign 策略,表明依据”对方”的主键来生成自己的主键，自己并不能独立生成主键. <param> 子元素指定使用当前持久化类的哪个属性作为 “对方”

  • 採用foreign主键生成器策略的一端添加 one-to-one 元素映射关联属性。其one-to-one属性还应添加 constrained=“true” 属性；还有一端添加one-to-one元素映射关联属性。
  • constrained(约束):指定为当前持久化类相应的数据库表的主键加入一个外键约束，引用被关联的对象(“对方”)所相应的数据库表主键



基于外键映射的 1-1

实例具体解释：

Department.java

package com.atguigu.hibernate.one2one.foreign;

public class Department {

	private Integer deptId;
	private String deptName;
	
	private Manager mgr;

	public Integer getDeptId() {
		return deptId;
	}

	public void setDeptId(Integer deptId) {
		this.deptId = deptId;
	}

	public String getDeptName() {
		return deptName;
	}

	public void setDeptName(String deptName) {
		this.deptName = deptName;
	}

	public Manager getMgr() {
		return mgr;
	}

	public void setMgr(Manager mgr) {
		this.mgr = mgr;
	}
	
}


Manager.java
package com.atguigu.hibernate.one2one.foreign;

public class Manager {

	private Integer mgrId;
	private String mgrName;
	
	private Department dept;

	public Integer getMgrId() {
		return mgrId;
	}

	public void setMgrId(Integer mgrId) {
		this.mgrId = mgrId;
	}

	public String getMgrName() {
		return mgrName;
	}

	public void setMgrName(String mgrName) {
		this.mgrName = mgrName;
	}

	public Department getDept() {
		return dept;
	}

	public void setDept(Department dept) {
		this.dept = dept;
	}
	
}


Department.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>

    <class name="com.atguigu.hibernate.one2one.foreign.Department" table="DEPARTMENTS">

        <id name="deptId" type="java.lang.Integer">
            <column name="DEPT_ID" />
            <generator class="native" />
        </id>
        
        <property name="deptName" type="java.lang.String">
            <column name="DEPT_NAME" />
        </property>
		
		<!-- 使用 many-to-one 的方式来映射 1-1 关联关系 -->
		<many-to-one name="mgr" class="com.atguigu.hibernate.one2one.foreign.Manager" 
			column="MGR_ID" unique="true"></many-to-one>	        
			        
    </class>
</hibernate-mapping>


Manager.hbm.xml
<?
xml version="1.0"?
>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <class name="com.atguigu.hibernate.one2one.foreign.Manager" table="MANAGERS">
        
        <id name="mgrId" type="java.lang.Integer">
            <column name="MGR_ID" />
            <generator class="native" />
        </id>
        
        <property name="mgrName" type="java.lang.String">
            <column name="MGR_NAME" />
        </property>
        
        <!-- 映射 1-1 的关联关系: 在相应的数据表中已经有外键了, 当前持久化类使用 one-to-one 进行映射 -->
        <!-- 
        	没有外键的一端须要使用one-to-one元素，该元素使用 property-ref 属性指定使用被关联实体主键以外的字段作为关联字段
         -->
        <one-to-one name="dept" 
        	class="com.atguigu.hibernate.one2one.foreign.Department"
        	property-ref="mgr"></one-to-one>
        
    </class>
    
</hibernate-mapping>


package com.atguigu.hibernate.one2one.foreign;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Date;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.jdbc.Work;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class HibernateTest {

	private SessionFactory sessionFactory;
	private Session session;
	private Transaction transaction;
	
	@Before
	public void init(){
		Configuration configuration = new Configuration().configure();
		ServiceRegistry serviceRegistry = 
				new ServiceRegistryBuilder().applySettings(configuration.getProperties())
				                            .buildServiceRegistry();
		sessionFactory = configuration.buildSessionFactory(serviceRegistry);
		
		session = sessionFactory.openSession();
		transaction = session.beginTransaction();
	}
	
	@After
	public void destroy(){
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
	
	@Test
	public void testGet2(){
		//在查询没有外键的实体对象时, 使用的左外连接查询, 一并查询出其关联的对象
		//并已经进行初始化. 
		Manager mgr = (Manager) session.get(Manager.class, 1);
		System.out.println(mgr.getMgrName()); 
		System.out.println(mgr.getDept().getDeptName()); 
	}
	
	@Test
	public void testGet(){
		//1. 默认情况下对关联属性使用懒载入
		Department dept = (Department) session.get(Department.class, 1);
		System.out.println(dept.getDeptName()); 
		
		//2. 所以会出现懒载入异常的问题. 
//		session.close();
//		Manager mgr = dept.getMgr();
//		System.out.println(mgr.getClass()); 
//		System.out.println(mgr.getMgrName()); 
		
		//3. 查询 Manager 对象的连接条件应该是 dept.manager_id = mgr.manager_id
		//而不应该是 dept.dept_id = mgr.manager_id
		Manager mgr = dept.getMgr();
		System.out.println(mgr.getMgrName()); 
		
		
	}
	
	@Test
	public void testSave(){
		
		Department department = new Department();
		department.setDeptName("DEPT-BB");
		
		Manager manager = new Manager();
		manager.setMgrName("MGR-BB");
		
		//设定关联关系
		department.setMgr(manager);
		manager.setDept(department);
		
		//保存操作
		//建议先保存没有外键列的那个对象. 这样会降低 UPDATE 语句
		session.save(department);
		session.save(manager);
		
	}
	
	

}


基于主键映射的 1-1

实例具体解释：

实体类不变和上面同样

Department.hbm.xml

<?
xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.atguigu.hibernate.one2one.primary">

    <class name="Department" table="DEPARTMENTS">

        <id name="deptId" type="java.lang.Integer">
            <column name="DEPT_ID" />
            <!-- 使用外键的方式来生成当前的主键 -->
            <generator class="foreign">
            	<!-- property 属性指定使用当前持久化类的哪一个属性的主键作为外键 -->
            	<param name="property">mgr</param>
            </generator>
        </id>
        
        <property name="deptName" type="java.lang.String">
            <column name="DEPT_NAME" />
        </property>
		
		<!--  
		採用 foreign 主键生成器策略的一端添加 one-to-one 元素映射关联属性,
		其 one-to-one 节点还应添加 constrained=true 属性, 以使当前的主键上加入外键约束
		-->
		<one-to-one name="mgr" class="Manager" constrained="true"></one-to-one>
					        
    </class>
</hibernate-mapping>


Manager.hbm.xml
<?
xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <class name="com.atguigu.hibernate.one2one.primary.Manager" table="MANAGERS">
        
        <id name="mgrId" type="java.lang.Integer">
            <column name="MGR_ID" />
            <generator class="native" />
        </id>
        
        <property name="mgrName" type="java.lang.String">
            <column name="MGR_NAME" />
        </property>
        
        <one-to-one name="dept" 
        	class="com.atguigu.hibernate.one2one.primary.Department"></one-to-one>
        
    </class>
    
</hibernate-mapping>


package com.atguigu.hibernate.one2one.primary;

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.After;
import org.junit.Before;
import org.junit.Test;

public class HibernateTest {

	private SessionFactory sessionFactory;
	private Session session;
	private Transaction transaction;
	
	@Before
	public void init(){
		Configuration configuration = new Configuration().configure();
		ServiceRegistry serviceRegistry = 
				new ServiceRegistryBuilder().applySettings(configuration.getProperties())
				                            .buildServiceRegistry();
		sessionFactory = configuration.buildSessionFactory(serviceRegistry);
		
		session = sessionFactory.openSession();
		transaction = session.beginTransaction();
	}
	
	@After
	public void destroy(){
		transaction.commit();
		session.close();
		sessionFactory.close();
	}
	
	@Test
	public void testGet2(){
		//在查询没有外键的实体对象时, 使用的左外连接查询, 一并查询出其关联的对象
		//并已经进行初始化. 
		Manager mgr = (Manager) session.get(Manager.class, 1);
		System.out.println(mgr.getMgrName()); 
		System.out.println(mgr.getDept().getDeptName()); 
	}
	
	@Test
	public void testGet(){
		//1. 默认情况下对关联属性使用懒载入
		Department dept = (Department) session.get(Department.class, 1);
		System.out.println(dept.getDeptName()); 
		
		//2. 所以会出现懒载入异常的问题. 
		Manager mgr = dept.getMgr();
		System.out.println(mgr.getMgrName()); 
	}
	
	@Test
	public void testSave(){
		
		Department department = new Department();
		department.setDeptName("DEPT-DD");
		
		Manager manager = new Manager();
		manager.setMgrName("MGR-DD");
		
		//设定关联关系
		manager.setDept(department);
		department.setMgr(manager);
		
		//保存操作
		//先插入哪一个都不会有多余的 UPDATE
		session.save(department);
		session.save(manager);
		
	}
}


posted on 2019-03-29 12:05  xfgnongmin  阅读(152)  评论(0)  编辑  收藏  举报

导航