Hibernate使用——一对一关联示例

weoln

2013-08-02

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一对一关联

一对一关联包括如下的两种类型：

1. 主键关联

2. 唯一外键关联

主键关联

一对一的主键关联形式，即两张关联表通过主键形成一对一映射关系。

下面是一个例子，oham 阵型与lulu阵型配对进行精神单挑，要求两组阵型人数相同，一对一PK： Hibernate使用——一对一关联示例

TOham.java

package learnHibernate.bean;

import java.io.Serializable;

public class TOham implements Serializable {
	private static final long serialVersionUID = -3474820872619575460L;
	
	private int id;
	private String name;
	private int groupId;
	private String meditation;
	
	private TLulu lu;

	public 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;
	}
	public int getGroupId() {
		return groupId;
	}
	public void setGroupId(int groupId) {
		this.groupId = groupId;
	}
	public TLulu getLu() {
		return lu;
	}
	public void setLu(TLulu lu) {
		this.lu = lu;
	}
	public String getMeditation() {
		return meditation;
	}
	public void setMeditation(String meditation) {
		this.meditation = meditation;
	}
}

TLulu.java

package learnHibernate.bean;

import java.io.Serializable;

public class TLulu implements Serializable {
	private static final long serialVersionUID = -252962688967803016L;
	
	private int id ;
	private String name;
	private String sixthSense;
	
	private TOham oh;

	public 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;
	}

	public TOham getOh() {
		return oh;
	}

	public void setOh(TOham oh) {
		this.oh = oh;
	}

	public String getSixthSense() {
		return sixthSense;
	}

	public void setSixthSense(String sixthSense) {
		this.sixthSense = sixthSense;
	}
}

TOham.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 package="learnHibernate.bean">
	<class name="TOham" table="t_oham">
		<id name="id" column="id" type="java.lang.Integer">
			<generator class="native"/>
		</id>
		
		<property name="name" 
				  column="name" 
				  type="java.lang.String" />
				  
		<property name="meditation" 
				  column="meditation" 
				  type="java.lang.String" />
				  
		<property name="groupId" 
				  column="group_id" 
				  type="java.lang.Integer" />
				  
				  
		<!-- 通过one-to-one节点，将Toham类与TLulu类相关联 -->		  
		<!-- cascade属性，当主控方执行操作的时候，关联对象是否执行同一操作，
		     如主控对象save-update-delete的时候，是否也同时对关联对象做相同动作，
		     此处为“all”，表示对关联类做同样的动作 -->		  
		<one-to-one name="lu"
					class="TLulu"
					cascade="all"
					outer-join="true">
		</one-to-one>

	</class>
</hibernate-mapping>

TLulu.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 package="learnHibernate.bean">
	<class name="TLulu" table="t_lulu">
		<id name="id" column="id" type="java.lang.Integer">
		
			<!-- t_oham与t_lulu采用了主键关联方式，所以关联的记录主键值必须保持同步 -->
			<!-- 所以只需为一张表设定主键生成器，而另一张表的主键与之共享相同的主键值 -->
			<!-- 此处用foreign类型的主键生成器，表示t_lulu的主键id同时为外键，
			             通过property：oh的TOham类表明关联的映射表为t_oham  -->
			<generator class="foreign">
				<param name="property">oh</param>
			</generator>
		</id>
		<!-- constrained为true，表明表t_oham的主键，被当前表t_lulu的外键关联着 -->
		<one-to-one name="oh"
					class="TOham" 
					constrained="true"/>
		
		<property name="name" 
				  column="name" 
				  type="java.lang.String" />
				  
		<property name="sixthSense" 
				  column="sixthsense" 
				  type="java.lang.String" />
				  
	</class>
</hibernate-mapping>

执行代码：

package learnHibernate;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.junit.Test;

import learnHibernate.bean.TLulu;
import learnHibernate.bean.TOham;
import learnHibernate.util.HibernateLocalUtil;

public class TestCase7 {

	@Test
	public void saveOrUpdateOhamlulu() {
		TOham oh = new TOham();
		oh.setName("Oham");
		oh.setMeditation("foresee");
		
		TLulu lu = new TLulu();
		lu.setName("Lulu");
		lu.setSixthSense("Perspective");
		
		//互相设置关联,否则会抛
		//org.hibernate.id.IdentifierGenerationException: attempted to assign id from null one-to-one property
		oh.setLu(lu);
		lu.setOh(oh);
		
		SessionFactory factory = HibernateLocalUtil.getSessionFactory();
		Session session = factory.openSession();
		Transaction tx = session.beginTransaction();
		
		//由于TOham映射文件中的one-to-one节点设置了cascade="all"
		//此处会被联级保存，若设置为"none"，则只保存TOham
		session.save(oh);
		
		tx.commit();
		session.close();
		
	}
	
	//@Test
	public void getOhamlulu() {
		SessionFactory factory = HibernateLocalUtil.getSessionFactory();
		Session session = factory.openSession();
		
		TOham oh = (TOham)session.load(TOham.class, new Integer(9));
		
		//TLulu lu = (TLulu)session.load(TLulu.class, new Integer(9));
		
		//System.out.println(oh.getName());
		//System.out.println(lu.getName());
		session.close();
	}
	
	
}

后台输出sql：

Hibernate: 
    insert 
    into
        t_oham
        (name, meditation, group_id) 
    values
        (?, ?, ?)
Hibernate: 
    insert 
    into
        t_lulu
        (name, sixthsense, id) 
    values
        (?, ?, ?)

然后执行查询代码：

TOham oh = (TOham)session.load(TOham.class, new Integer(9));
		//因为TOham默认为延迟加载，调用对象时才会执行查询数据库
		System.out.println(oh.getName());

后台输出sql：

Hibernate: 
    select
        toham0_.id as id0_1_,
        toham0_.name as name0_1_,
        toham0_.meditation as meditation0_1_,
        toham0_.group_id as group4_0_1_,
        tlulu1_.id as id1_0_,
        tlulu1_.name as name1_0_,
        tlulu1_.sixthsense as sixthsense1_0_ 
    from
        t_oham toham0_ 
    left outer join
        t_lulu tlulu1_ 
            on toham0_.id=tlulu1_.id 
    where
        toham0_.id=?

注意：若将TOham.hbm.xml的outer-join设置为“false”，重新执行查询代码，结果：

后台输出sql：

Hibernate: 
    select
        toham0_.id as id0_0_,
        toham0_.name as name0_0_,
        toham0_.meditation as meditation0_0_,
        toham0_.group_id as group4_0_0_ 
    from
        t_oham toham0_ 
    where
        toham0_.id=?
Hibernate: 
    select
        tlulu0_.id as id1_0_,
        tlulu0_.name as name1_0_,
        tlulu0_.sixthsense as sixthsense1_0_ 
    from
        t_lulu tlulu0_ 
    where
        tlulu0_.id=?

这时，再把TLulu.hbm.xml的constrained设置为“false”，执行代码，结果：

Hibernate: 
    select
        toham0_.id as id0_0_,
        toham0_.name as name0_0_,
        toham0_.meditation as meditation0_0_,
        toham0_.group_id as group4_0_0_ 
    from
        t_oham toham0_ 
    where
        toham0_.id=?
Hibernate: 
    select
        tlulu0_.id as id1_1_,
        tlulu0_.name as name1_1_,
        tlulu0_.sixthsense as sixthsense1_1_,
        toham1_.id as id0_0_,
        toham1_.name as name0_0_,
        toham1_.meditation as meditation0_0_,
        toham1_.group_id as group4_0_0_ 
    from
        t_lulu tlulu0_ 
    left outer join
        t_oham toham1_ 
            on tlulu0_.id=toham1_.id 
    where
        tlulu0_.id=?

说实话，在下不太明白constrained的具体作用，只知道当在采用主键关联的方式去做一对一关联时，从表（这里的例子t_lulu）的映射配置里id 的foreign类generator必须与constrained设置为true配对出现。

注意的一点是主从关系，我一般这样理解，持有外键的表是从表，是关联方，而被关联的表是主表，是主控方，被关联方，在hibernate的映射当中主从理清关系很重要，因为涉及级联操作，弄不好会造成逻辑混乱。

唯一外键关联

顾名思义，通过非主键的唯一外键来做一对一关联，现在举一例子：先前oham与lulu两阵型心灵单挑进行中，可惜两组总体水平相去甚远，现在oham组要求组内每人可以召唤帮托，但为兼顾公平，现在只允许每人召唤一个，并且只能是cancan类型的，还有不能召唤同一人。。。

Hibernate使用——一对一关联示例
TOham.java：

package learnHibernate.bean;

import java.io.Serializable;

public class TOham implements Serializable {
	private static final long serialVersionUID = -3474820872619575460L;
	
	private int id;
	private String name;
	private int groupId;
	private String meditation;
	
	private TLulu lu;
	
	private TCancan can;

	public 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;
	}
	public int getGroupId() {
		return groupId;
	}
	public void setGroupId(int groupId) {
		this.groupId = groupId;
	}
	public TLulu getLu() {
		return lu;
	}
	public void setLu(TLulu lu) {
		this.lu = lu;
	}
	public String getMeditation() {
		return meditation;
	}
	public void setMeditation(String meditation) {
		this.meditation = meditation;
	}
	public TCancan getCan() {
		return can;
	}
	public void setCan(TCancan can) {
		this.can = can;
	}
}

TCancan.java：

package learnHibernate.bean;

public class TCancan {

	private int id;
	private String name;
	private String think;
	
	private TOham oh;
	
	public 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;
	}
	public String getThink() {
		return think;
	}
	public void setThink(String think) {
		this.think = think;
	}
	public TOham getOh() {
		return oh;
	}
	public void setOh(TOham oh) {
		this.oh = oh;
	}
}

TOham.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 package="learnHibernate.bean">
	<class name="TOham" table="t_oham">
		<id name="id" column="id" type="java.lang.Integer">
			<generator class="native"/>
		</id>
		
		<property name="name" 
				  column="name" 
				  type="java.lang.String" />
				  
		<property name="meditation" 
				  column="meditation" 
				  type="java.lang.String" />
				  
		<property name="groupId" 
				  column="group_id" 
				  type="java.lang.Integer" />
				  
		<one-to-one name="lu"
					class="TLulu"
					cascade="all"
					outer-join="true">
		</one-to-one>
		
		<!-- 外键关联，一般是多对一的，唯一外键关联只是其中一个特例，
		  	  所以此处用了many-to-one，并设置unqiue为true，表明此外键唯一 -->
		<many-to-one name="can" 
		             class="TCancan"
		             column="friend_id"
		             unique="true"/>

	</class>
</hibernate-mapping>

TCancan.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 package="learnHibernate.bean">
	<class name="TCancan" table="t_cancan">
		<id name="id" column="id" type="java.lang.Integer">
			<generator class="native" />
		</id>
		
		<!--<one-to-one name="oh"
					class="TOham"
					property-ref="can" />-->
		
		<property name="name" 
				  column="name" 
				  type="java.lang.String" />
				  
		<property name="think" 
				  column="think" 
				  type="java.lang.String" />
				  
	</class>
</hibernate-mapping>

执行代码：

TOham oh = (TOham)session.load(TOham.class, new Integer(6));
		System.out.println(oh.getCan().getName());

结果：

Hibernate: 
    select
        toham0_.id as id0_1_,
        toham0_.name as name0_1_,
        toham0_.meditation as meditation0_1_,
        toham0_.group_id as group4_0_1_,
        toham0_.friend_id as friend5_0_1_,
        tlulu1_.id as id1_0_,
        tlulu1_.name as name1_0_,
        tlulu1_.sixthsense as sixthsense1_0_ 
    from
        t_oham toham0_ 
    left outer join
        t_lulu tlulu1_ 
            on toham0_.id=tlulu1_.id 
    where
        toham0_.id=?
Hibernate: 
    select
        tcancan0_.id as id2_0_,
        tcancan0_.name as name2_0_,
        tcancan0_.think as think2_0_ 
    from
        t_cancan tcancan0_ 
    where
        tcancan0_.id=?

此处要注意的是因为先前的例子我们做了主键一对一关联，所以此处left join了t_lulu表，若是用单纯的唯一外键映射例子做实验，此处的sql可能是left outer join的，可以去试试，因为many-to-one的outer-join默认为true。这是hibernate底层优化的结果。

另外注意若不调用oh下面的can对象的话hibernate不会去执行查询t_canca的操作。

此处在hibernate的映射层面是个单向的关联，也就是说，执行下面代码：

TCancan can = (TCancan)session.load(TCancan.class, new Integer(1));
		System.out.println(can.getOh());

结果是hibernate只会查询t_cancan表，不会去查t_oham表：

Hibernate: 
    select
        tcancan0_.id as id2_0_,
        tcancan0_.name as name2_0_,
        tcancan0_.think as think2_0_ 
    from
        t_cancan tcancan0_ 
    where
        tcancan0_.id=?

若我们把TCancan.hbm.xml中的one-to-one节点的注释放开：

<one-to-one name="oh"
					class="TOham"
					property-ref="can" />

其中property-ref指定为TOham的属性名为can，意思是TOham的can就是关联着本类TCancan的。这样就实现了映射层面的双向关联。

在执行代码：

TCancan can = (TCancan)session.load(TCancan.class, new Integer(1));
		System.out.println(can.getOh());

结果把t_cancan关联进来了：

Hibernate: 
    select
        tcancan0_.id as id2_2_,
        tcancan0_.name as name2_2_,
        tcancan0_.think as think2_2_,
        toham1_.id as id0_0_,
        toham1_.name as name0_0_,
        toham1_.meditation as meditation0_0_,
        toham1_.group_id as group4_0_0_,
        toham1_.friend_id as friend5_0_0_,
        tlulu2_.id as id1_1_,
        tlulu2_.name as name1_1_,
        tlulu2_.sixthsense as sixthsense1_1_ 
    from
        t_cancan tcancan0_ 
    left outer join
        t_oham toham1_ 
            on tcancan0_.id=toham1_.friend_id 
    left outer join
        t_lulu tlulu2_ 
            on toham1_.id=tlulu2_.id 
    where
        tcancan0_.id=?

此处就引申了一个问题，若一个实体的映射关联多了，就不能总让其join来join去了，那么就要考虑如何设置映射配置，使得性能最优化。。。

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