一、概述

我們以Company與Address類為例，介紹映射一對一關聯關系的方法。
一對一的關聯方法有兩種
-按照外鍵映射：兩個表任意一個表定義一個外鍵，來關聯另一個表。
-按照主鍵映射：一個表的主鍵同時作為外鍵，和另一個表的主鍵保持一致。

二、按照外鍵映射

（1）創建實體類

            public class Company {
                private Integer id;
                private String name;
                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;
                }

            } 

            public class Address {
                private Integer id;
                private String name;
                private Company company;
                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 Company getCompany() {
                    return company;
                }
                public void setCompany(Company company) {
                    this.company = company;
                }

            } 

　　（2）我們配置映射文件，我們在Company這一方設置外鍵來關聯Address 有外鍵的一方要使用<many-to-one>元素來配置。

        Company.hbm.xml
         <hibernate-mapping >
            <class name="com.cad.domain.Company" table="company">
                <id name="id" column="id">
                    <generator class="native"></generator>
                </id>
                <property name="name" column="name"></property> 
                <!--column指定外鍵，unique指定外鍵唯一約束，設為true，就可以表達Company和Address對象之間的一對一關聯-->
                <many-to-one name="address" class="com.cad.domain.Address" column="aid" unique="true"></many-to-one>
            </class>
         </hibernate-mapping>   

         Address.hbm.xml 
         <hibernate-mapping >
            <class name="com.cad.domain.Address" table="address">
                <id name="id" column="id">
                    <generator class="native"></generator>
                </id>
                <property name="name" column="name"></property> 
                <!--property-ref屬性指定通過從Company的address屬性來查找自己-->
                <one-to-one name="Company" class="com.cad.domain.Company" property-ref="address"></one-to-one>
            </class>
         </hibernate-mapping>  

　　測試：

                 public class Demo {

                    private Session session;

                    @Test
                    public void test() {
                        //讀取配置文件
                        Configuration conf=new Configuration().configure();

                        //根據配置創建factory
                        SessionFactory sessionfactory=conf.buildSessionFactory();
                        session = sessionfactory.openSession(); 
                         Transaction ts=session.beginTransaction();
                        Company c=new Company();
                        c.setName("百度");
                        Address a=new Address();
                        a.setName("深圳");
                        c.setAddress(a);
                        a.setCompany(c);

                        session.save(a);
                        session.save(c); 

                        ts.commit();
                        session.close();
                        sessionfactory.close();
                    }

                }

            默認情況下，一對一關聯采用迫切左外連接檢索策略。

三、按照主鍵映射

    實體類不變，我們編寫一下配置文件
    address的表的id字段既是主鍵又是外鍵.

        編寫配置文件
        Company.hbm.xml 
         <hibernate-mapping >
            <class name="com.cad.domain.Company" table="company">
                <id name="id" column="id">
                    <generator class="native"></generator>
                </id>
                <property name="name" column="name"></property>
                <one-to-one name="address" class="com.cad.domain.Address" ></one-to-one>
            </class>
         </hibernate-mapping> 

        Address.hbm.xml 
         <hibernate-mapping >
            <class name="com.cad.domain.Address" table="address">
                <id name="id" column="id">
                    <!--必須使用foreign標識符生成策略，還要指定哪個對象共享OID-->
                    <generator class="foreign">
                        <param name="property">company</param>
                    </generator>
                </id>
                <property name="name" column="name"></property>
                <!--constrained屬性設為true，說明主鍵同時作為外鍵-->
                <one-to-one name="company" class="com.cad.domain.Company" constrained="true"></one-to-one>
            </class>
         </hibernate-mapping>  

（十）Hibernate的一對一關聯關系