Hibernate关联关系映射—1对1详解编程语言

1对1
Hibernate的1对1关联关系映射有两种
1 主表主键与从表主键，形成主外键关系(从表的主键又是外键)
2 主表主键与从表外键(必须唯一unique)，形成主外键关系

1对1中PO使用的一个，只是hbm.xml映射存在两次写法

1对1分析：

实例：公司Company ： 地址Address

jvava bean

Address.java:

package com.my.bean; 
 
public class Address { 
 
    private Integer id; 
    private String addr; 
 
    //第一个地址 属于一个公司 
    private Company company; 
 
    public Integer getId() { 
        return id; 
    } 
 
    public void setId(Integer id) { 
        this.id = id; 
    } 
 
    public String getAddr() { 
        return addr; 
    } 
 
    public void setAddr(String addr) { 
        this.addr = addr; 
    } 
 
    public Company getCompany() { 
        return company; 
    } 
 
    public void setCompany(Company company) { 
        this.company = company; 
    } 
 
} 

Company.java:

package com.my.bean; 
 
public class Company { 
 
    private Integer id; 
    private String name; 
 
    //第一个公司只有一个地址 
    private Address address; 
 
    public Integer getId() { 
        return id; 
    } 
 
    public void setId(Integer id) { 
        this.id = id; 
    } 
 
    public String getName() { 
        return name; 
    } 
 
    public void setName(String name) { 
        this.name = name; 
    } 
 
    public Address getAddress() { 
        return address; 
    } 
 
    public void setAddress(Address address) { 
        this.address = address; 
    } 
 
} 

主表主键与从表主键，形成主外键关系(从表的主键又是外键)

Address.hbm.xml

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE hibernate-mapping PUBLIC  
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 
<hibernate-mapping> 
    <class name="com.my.bean.Address" table="t_address_pk"> 
        <id name="id"> 
            <!-- 从表主键 又是主表的外键 --> 
            <generator class="foreign"> 
                <param name="property">company</param> 
            </generator> 
        </id> 
        <property name="addr"></property> 
 
        <!-- 1对1 ,此项确定提供给约束使用的 --> 
        <one-to-one name="company" class="com.my.bean.Company" constrained="true"></one-to-one> 
 
    </class> 
 
</hibernate-mapping>

Company.hbm.xml

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE hibernate-mapping PUBLIC  
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 
<hibernate-mapping> 
    <class name="com.my.bean.Company" table="t_company_pk"> 
        <id name="id"> 
            <generator class="native"></generator> 
        </id> 
        <property name="name"></property> 
 
        <!-- 1对1 --> 
        <one-to-one name="address" class="com.my.bean.Address"></one-to-one> 
    </class> 
 
</hibernate-mapping>

主表主键与从表外键(必须唯一unique)，形成主外键关系

Address.hbm.xml

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE hibernate-mapping PUBLIC  
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 
<hibernate-mapping> 
    <class name="com.my.bean.Address" table="t_address"> 
        <id name="id"> 
            <generator class="native"></generator> 
        </id> 
        <property name="addr"></property> 
 
        <!-- 特例：本身多对1，但此时要是地址i必须唯一 ， column指定就是外键的名称--> 
        <many-to-one name="company" class="com.my.bean.Company" column="company_id" unique="true"></many-to-one> 
 
    </class> 
 
</hibernate-mapping>

Company.hbm.xml

<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE hibernate-mapping PUBLIC  
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 
<hibernate-mapping> 
    <class name="com.my.bean.Company" table="t_company"> 
        <id name="id"> 
            <generator class="native"></generator> 
        </id> 
        <property name="name"></property> 
 
        <!-- foreign-key 直接指定外键的值，property-ref通过属性获得对应的表中外键名称 --> 
        <one-to-one name="address" class="com.my.bean.Address"  foreign-key="company_id"></one-to-one> 
 
    </class> 
 
</hibernate-mapping>

测试类：

package com.my.bean; 
 
 
import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.hibernate.cfg.Configuration; 
import org.junit.Test; 
 
public class TestOneToOne { 
 
    private SessionFactory sessionFactory = new Configuration() 
                                .configure() 
                                .addClass(Company.class) 
                                .addClass(Address.class) 
                                .buildSessionFactory(); 
 
    @Test 
    public void demo01(){ 
        Session session = sessionFactory.openSession(); 
 
        session.close(); 
    } 
 
}