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

巴特西

Hibernate映射一对一关联关系

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