Hibernate的一对一映射

一、创建Java工程，新建Lib文件夹，加入Hibernate和数据库（如MySql、Oracle、SqlServer等）的Jar包，创建 hibernate.cfg.xml 文件，并配置，配置项如下：

<?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">
<hibernate-configuration>
    <session-factory>
    
        <!-- 配置连接数据库的基本信息 -->
        <property name="connection.username">root</property>
        <property name="connection.password"></property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- <property name="connection.url">jdbc:mysql:///mis</property> -->
        <property name="connection.url">
            <!-- 解决Mysql插入中文乱码的问题 -->
            <![CDATA[jdbc:mysql://localhost:3306/mis?useUnicode=true&characterEncoding=utf8]]>
        </property>


        <!-- 配置 hibernate 的基本信息 -->
        <!-- hibernate 所使用的数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property>

        <!-- 执行操作时是否在控制台打印 SQL -->
        <property name="show_sql">true</property>

        <!-- 是否对 SQL 进行格式化 -->
        <property name="format_sql">true</property>

        <!-- 指定自动生成数据表的策略 -->
        <property name="hbm2ddl.auto">update</property>
        
        <!-- 设置 Hibernate 的事务隔离级别 2:读已提交的记录-->
        <property name="connection.isolation">2</property>
        
        <!-- 删除对象后, 使其 OID 置为 null -->
        <property name="use_identifier_rollback">true</property>
        
        <!-- 配置 C3P0 数据源 -->
        <property name="hibernate.c3p0.max_size">10</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="c3p0.acquire_increment">2</property>
        
        <property name="c3p0.idle_test_period">2000</property>
        <property name="c3p0.timeout">2000</property>
        
        <property name="c3p0.max_statements">10</property>
        
        <!-- 设定 JDBC 的 Statement 读取数据的时候每次从数据库中取出的记录条数 -->
        <property name="hibernate.jdbc.fetch_size">100</property>
        
        <!-- 设定对数据库进行批量删除，批量更新和批量插入的时候的批次大小 -->
        <property name="jdbc.batch_size">30</property>

        <!-- 指定关联的 .hbm.xml 文件 -->
        <!-- 
        <mapping resource="com/mcs/hibernate/entities/News.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/Worker.hbm.xml" />
        
        <mapping resource="com/mcs/hibernate/entities/n21/Customer.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/n21/Order.hbm.xml" />
         -->
         
        <mapping resource="com/mcs/hibernate/entities/n21/both/Customer.hbm.xml" />
        <mapping resource="com/mcs/hibernate/entities/n21/both/Order.hbm.xml" />

    </session-factory>

</hibernate-configuration>

二、基于外键的一对一映射

1、创建Java实体类

package com.mcs.hibernate.entities.onetoone.foreign;

public class Department {
    
    private Integer departmentId;
    private String departmentName;
    
    private Manager manager;

    public Integer getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Integer departmentId) {
        this.departmentId = departmentId;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }

    public Manager getManager() {
        return manager;
    }

    public void setManager(Manager manager) {
        this.manager = manager;
    }
    
    

}

package com.mcs.hibernate.entities.onetoone.foreign;

public class Manager {
    
    private Integer managerId;
    private String managerName;
    
    private Department department;

    public Integer getManagerId() {
        return managerId;
    }

    public void setManagerId(Integer managerId) {
        this.managerId = managerId;
    }

    public String getManagerName() {
        return managerName;
    }

    public void setManagerName(String managerName) {
        this.managerName = managerName;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }
    
    

}

2、根据实体类创建对应的 hbm.xml文件

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.onetoone.foreign.Department" table="DEPARTMENTS">
        <id name="departmentId" type="java.lang.Integer">
            <column name="DEPARTMENT_ID" />
            <generator class="native" />
        </id>
        <property name="departmentName" type="java.lang.String">
            <column name="DEPARTMENT_NAME" />
        </property>
        
        <!-- 使用 many-to-one 的方式来映射 1-1 关联关系 -->
        <many-to-one name="manager" 
            class="com.mcs.hibernate.entities.onetoone.foreign.Manager"
            column="MANAGER_ID"
            unique="true"></many-to-one>
    </class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.onetoone.foreign.Manager" table="MANAGERS">
        <id name="managerId" type="java.lang.Integer">
            <column name="MANAGER_ID" />
            <generator class="native" />
        </id>
        <property name="managerName" type="java.lang.String">
            <column name="MANAGER_NAME" />
        </property>
        
        <!-- 映射 1-1 的关联关系: 在对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 -->
        <!-- 
            没有外键的一端需要使用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="department" 
            class="com.mcs.hibernate.entities.onetoone.foreign.Department"
            property-ref="manager">
        </one-to-one>
    </class>
</hibernate-mapping>

注：

　　1、在有外键的一端需要使用many-to-one元素，该元素使用 unique="true" 属性来约束唯一值，并指定外键栏 column="MANAGER_ID"

　　2、没有外键的一端需要使用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

　　3、在保存操作中，建议先保存没有外键列的那个对象. 这样会减少 UPDATE 语句

　　4、默认情况下对关联属性使用懒加载，注意可能会出现懒加载异常的问题。

　　5、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。

三、基于主键的一对一映射

1、创建Java实体类 

package com.mcs.hibernate.entities.onetoone.primary;

public class Department {
    
    private Integer departmentId;
    private String departmentName;
    
    private Manager manager;

    public Integer getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Integer departmentId) {
        this.departmentId = departmentId;
    }

    public String getDepartmentName() {
        return departmentName;
    }

    public void setDepartmentName(String departmentName) {
        this.departmentName = departmentName;
    }

    public Manager getManager() {
        return manager;
    }

    public void setManager(Manager manager) {
        this.manager = manager;
    }
    
    

}

package com.mcs.hibernate.entities.onetoone.primary;

public class Manager {
    
    private Integer managerId;
    private String managerName;
    
    private Department department;

    public Integer getManagerId() {
        return managerId;
    }

    public void setManagerId(Integer managerId) {
        this.managerId = managerId;
    }

    public String getManagerName() {
        return managerName;
    }

    public void setManagerName(String managerName) {
        this.managerName = managerName;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }
    
    

}

2、根据实体类创建对应的 hbm.xml文件

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.onetoone.primary.Department" table="DEPARTMENTS">
        <id name="departmentId" type="java.lang.Integer">
            <column name="DEPARTMENT_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">manager</param>
            </generator>
        </id>
        <property name="departmentName" type="java.lang.String">
            <column name="DEPARTMENT_NAME" />
        </property>
        
        <!--  
        采用 foreign 主键生成器策略的一端增加 one-to-one 元素映射关联属性,
        其 one-to-one 节点还应增加 constrained=true 属性, 以使当前的主键上添加外键约束
        -->
        <one-to-one name="manager" 
            class="com.mcs.hibernate.entities.onetoone.primary.Manager"
            constrained="true">
        </one-to-one>
    </class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-10-28 13:38:17 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="com.mcs.hibernate.entities.onetoone.primary.Manager" table="MANAGERS">
        <id name="managerId" type="java.lang.Integer">
            <column name="MANAGER_ID" />
            <generator class="native" />
        </id>
        <property name="managerName" type="java.lang.String">
            <column name="MANAGER_NAME" />
        </property>

        <one-to-one name="department" 
            class="com.mcs.hibernate.entities.onetoone.primary.Department">
        </one-to-one>
    </class>
</hibernate-mapping>

注：

　　1、其中一端会使用另外一端的主键做为主键，另外一端代码采用 foreign 主键生成器策略的一端增加 one-to-one 元素映射关联属性,其 one-to-one 节点还应增加 constrained=true 属性, 以使当前的主键上添加外键约束。　

　　2、在保存操作中，建议先保存没有外键列的那个对象. 这样会减少 UPDATE 语句

　　3、默认情况下对关联属性使用懒加载，注意可能会出现懒加载异常的问题。