Hibernate映射一对一关联关系

映射一对一关联

Hibernate提供了两种映射一对一关联关系的方式，分别是按照外键映射和按照主键映射。

下面是员工表和档案信息表（员工和档案表之间的关系是一对一的关系）

　　 档案表（dept）

 public class Dept {
     private Integer deptid;
     private String mystreet;
     private Emp emp;

     public Dept() {
     }

     public Dept(Integer deptid, String mystreet, Emp emp) {
         this.deptid = deptid;
         this.mystreet = mystreet;
         this.emp = emp;
     }
     public Integer getDeptid() {
         return deptid;
     }
     public void setDeptid(Integer deptid) {
         this.deptid = deptid;
     }
     public String getMystreet() {
         return mystreet;
     }
     public void setMystreet(String mystreet) {
         this.mystreet = mystreet;
     }
     public Emp getEmp() {
         return emp;
     }
     public void setEmp(Emp emp) {
         this.emp = emp;
     }

 }

员工表（emp）

 public class Emp {
     private Integer empid;
     private String myname;
     private Dept dept;

     public Emp() {
     }

     public Emp(Integer empid, String myname, Dept dept) {
         this.empid = empid;
         this.myname = myname;
         this.dept = dept;
     }
     public Integer getEmpid() {
         return empid;
     }
     public void setEmpid(Integer empid) {
         this.empid = empid;
     }
     public String getMyname() {
         return myname;
     }
     public void setMyname(String myname) {
         this.myname = myname;
     }
     public Dept getDept() {
         return dept;
     }
     public void setDept(Dept dept) {
         this.dept = dept;
     }
 }

下面是第一种方案是按照主键映射

Emp的配置文件

 <?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 package="cn.rm.onetoone_pk">
         <class name="Emp" table="EMP2016">
             <id name="empid" column="EMPID" type="int">
                 <generator class="sequence">
                     <param name="sequence">sq_id</param>
                 </generator>
             </id>
             <property name="myname" column="MYNAME" type="string"></property>
             <one-to-one name="dept" class="Dept" property-ref="emp"></one-to-one>
             <!-- property-ref为emp表明了Dept的emp属性建立了从Emp对象到Dept对象的关联  -->
         </class>

     </hibernate-mapping>

Dept的配置文件

 <?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 package="cn.rm.onetoone_pk">
         <class name="Dept" table="DEPT2016">
             <id name="deptid" column="DEPTID" type="int">
                 <generator class="sequence">
                     <param name="sequence">hb_ids</param>
                 </generator>
             </id>
             <property name="mystreet" column="MYSTREET" type="string"></property>
             <many-to-one name="emp" class="Emp" cascade="all" unique="true" column="RESUSERID"></many-to-one>
             <!-- cascade属性为all表示对本表的增 删 改 相关联的表都会自动更新 unique， 属性为true 表示唯一约束  column="RESUSERID" dept表的公共列-->
         </class>
     </hibernate-mapping>

这种方案的特点是：会在Dept表中增加一列 column="RESUSERID"这里就是与Emp相关联的列

第二种方案是按照外键映射

Emp的配置文件

 <?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 package="cn.rm.onetoone_fk">
         <class name="Emp" table="EMP2016fk">
             <id name="empid" column="EMPID" type="int">
                 <generator class="foreign">
                     <param name="property">dept</param>
                 </generator>
             </id>
             <property name="myname" column="MYNAME" type="string"></property>
             <one-to-one name="dept" class="Dept" constrained="true"></one-to-one>
             <!--  constrained="true" 表示Emp表中的主键同时作为外键参照Emp表中的主键 -->
         </class>
     </hibernate-mapping>

Dept的配置文件

 <?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 package="cn.rm.onetoone_fk">
         <class name="Dept" table="DEPT2016fk">
             <id name="deptid" column="DEPTID" type="int">
                 <generator class="sequence">
                     <param name="sequence">hb_ids</param>
                 </generator>
             </id>
             <property name="mystreet" column="MYSTREET" type="string"></property>
             <one-to-one name="emp" class="Emp" cascade="all" ></one-to-one>
         </class>
     </hibernate-mapping>

这种方案的特点是员工表的主键和Dept表中的主键是相同的也就是Emp表和Dept表共享同一个OID