hibernate中one-to-one的应用介绍

第一种:双向one-to-one,两边都配置one-to-one且数据库有主外键关系，外键又是子表的主键（此时month表id为主键，creater表id为外键对映关系）

mysql数据库表结构:

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CREATE TABLE `month` (  `id` INTEGER(11) NOT NULL AUTO_INCREMENT,  `name` VARCHAR(20) COLLATE utf8_general_ci NOT NULL DEFAULT '',  `total` FLOAT(9,2) DEFAULT '0.00',  PRIMARY KEY (`id`))ENGINE=InnoDBAUTO_INCREMENT=0 CHARACTER SET 'utf8' COLLATE 'utf8_general_ci'

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CREATE TABLE `creater` (  `id` INTEGER(11) NOT NULL,  `name` VARCHAR(100) COLLATE utf8_general_ci DEFAULT NULL,  PRIMARY KEY (`id`),  CONSTRAINT `creater_fk` FOREIGN KEY (`id`) REFERENCES `month` (`id`))ENGINE=InnoDBCHARACTER SET 'utf8' COLLATE 'utf8_general_ci'

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Month.hbm.xml

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<?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 package="com.xuyi.modal">    <class name="Month" table="month" catalog="myweb">        <id name="id" type="java.lang.Integer">            <column name="id" />            <generator />        </id>        <property name="name" type="java.lang.String">            <column name="name" length="20" not-null="true" />        </property>         <property name="total" type="java.lang.Float">            <column name="total"/>        </property>        <one-to-one name="creater" cascade="all"></one-to-one>        <set name="things" inverse="true" lazy="false" cascade="all-delete-orphan">        <key column="monthid"/>        <one-to-many name="code"><?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 package="com.xuyi.modal"> <class catalog="myweb" name="Creater" table="creater">  <id name="id" type="java.lang.Integer">   <column name="id"/>   <generator type="java.lang.String">   <column length="100" name="name"/>  </property>     <one-to-one name="month" constrained="true"></one-to-one> </class></hibernate-mapping>

测试代码:

com.xuyi.modal.Month m = new com.xuyi.modal.Month();m.setName("2011年12月");m.setTotal(10f);Creater c = new Creater();c.setName("sina");c.setMonth(m);m.setCreater(c);getHibernateTemplate().save(m);

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第二种:在主键表使用one-to-one,外键表使用many-to-one,此种情况外键较第一种情况有所区别,反过来主键为creater表的id并且改为自增字段（第一种的时候此id字段为month的外键，此种情况变为主键）,外键为month表新增字段creater_id（注意数据库要加这个字段唯一约束）。

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CREATE TABLE `month` (  `id` INTEGER(11) NOT NULL AUTO_INCREMENT,  `creater_id` INTEGER(11) NOT NULL,  `name` VARCHAR(20) COLLATE utf8_general_ci NOT NULL DEFAULT '',  `total` FLOAT(9,2) DEFAULT '0.00',  PRIMARY KEY (`id`),  UNIQUE KEY `creater_id` (`creater_id`),  CONSTRAINT `month_fk` FOREIGN KEY (`creater_id`) REFERENCES `creater` (`id`))ENGINE=InnoDBAUTO_INCREMENT=0 CHARACTER SET 'utf8' COLLATE 'utf8_general_ci'

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CREATE TABLE `creater` (  `id` INTEGER(11) NOT NULL AUTO_INCREMENT,  `name` VARCHAR(100) COLLATE utf8_general_ci DEFAULT NULL,  PRIMARY KEY (`id`))ENGINE=InnoDBAUTO_INCREMENT=0 CHARACTER SET 'utf8' COLLATE 'utf8_general_ci'

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Month.hbm.xml

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<?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 package="com.xuyi.modal">    <class name="Month" table="month" catalog="myweb">        <id name="id" type="java.lang.Integer">            <column name="id" />            <generator />        </id>        <property name="name" type="java.lang.String">            <column name="name" length="20" not-null="true" />        </property>         <property name="total" type="java.lang.Float">            <column name="total"/>        </property>        <many-to-one name="creater" column="creater_id" cascade="all" unique="true"></many-to-one>        <set name="things" inverse="true" lazy="false" cascade="all-delete-orphan">        <key column="monthid"/>        <one-to-many name="code"><?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 package="com.xuyi.modal"> <class catalog="myweb" name="Creater" table="creater">  <id name="id" type="java.lang.Integer">   <column name="id"/>   <generator type="java.lang.String">   <column length="100" name="name"/>  </property>     <one-to-one name="month" property-ref="creater"></one-to-one> </class></hibernate-mapping>

测试代码：（同上）

com.xuyi.modal.Month m = new com.xuyi.modal.Month();m.setName("2012年4月");m.setTotal(10f);Creater c = new Creater();c.setName("4");c.setMonth(m);m.setCreater(c);getHibernateTemplate().save(m);

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一般情况下建议用第一种，而且在数据库设计的时候也相比第二种情况要少建一个字段和一个约束。