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）

 1 public class Dept {
 2     private Integer deptid;
 3     private String mystreet;
 4     private Emp emp;
 5             
 6     public Dept() {
 7     }
 8     
 9     public Dept(Integer deptid, String mystreet, Emp emp) {
10         this.deptid = deptid;
11         this.mystreet = mystreet;
12         this.emp = emp;
13     }
14     public Integer getDeptid() {
15         return deptid;
16     }
17     public void setDeptid(Integer deptid) {
18         this.deptid = deptid;
19     }
20     public String getMystreet() {
21         return mystreet;
22     }
23     public void setMystreet(String mystreet) {
24         this.mystreet = mystreet;
25     }
26     public Emp getEmp() {
27         return emp;
28     }
29     public void setEmp(Emp emp) {
30         this.emp = emp;
31     }
32     
33 }

员工表（emp）

 1 public class Emp {
 2     private Integer empid;
 3     private String myname;
 4     private Dept dept;
 5 
 6     public Emp() {
 7     }
 8     
 9     public Emp(Integer empid, String myname, Dept dept) {
10         this.empid = empid;
11         this.myname = myname;
12         this.dept = dept;
13     }
14     public Integer getEmpid() {
15         return empid;
16     }
17     public void setEmpid(Integer empid) {
18         this.empid = empid;
19     }
20     public String getMyname() {
21         return myname;
22     }
23     public void setMyname(String myname) {
24         this.myname = myname;
25     }
26     public Dept getDept() {
27         return dept;
28     }
29     public void setDept(Dept dept) {
30         this.dept = dept;
31     }
32 }

下面是第一种方案是按照主键映射

Emp的配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5     <hibernate-mapping package="cn.rm.onetoone_pk">
 6         <class name="Emp" table="EMP2016">
 7             <id name="empid" column="EMPID" type="int">
 8                 <generator class="sequence">
 9                     <param name="sequence">sq_id</param>
10                 </generator>
11             </id>
12             <property name="myname" column="MYNAME" type="string"></property>
13             <one-to-one name="dept" class="Dept" property-ref="emp"></one-to-one>
14             <!-- 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  -->
15         </class>
16         
17     </hibernate-mapping>

View Code

Dept的配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5     <hibernate-mapping package="cn.rm.onetoone_pk">
 6         <class name="Dept" table="DEPT2016">
 7             <id name="deptid" column="DEPTID" type="int">
 8                 <generator class="sequence">
 9                     <param name="sequence">hb_ids</param>
10                 </generator>
11             </id>
12             <property name="mystreet" column="MYSTREET" type="string"></property>
13             <many-to-one name="emp" class="Emp" cascade="all" unique="true" column="RESUSERID"></many-to-one>
14             <!-- 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-->
15         </class>
16     </hibernate-mapping>

View Code

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

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5     <hibernate-mapping package="cn.rm.onetoone_fk">
 6         <class name="Emp" table="EMP2016fk">
 7             <id name="empid" column="EMPID" type="int">
 8                 <generator class="foreign">
 9                     <param name="property">dept</param>
10                 </generator>
11             </id>
12             <property name="myname" column="MYNAME" type="string"></property>
13             <one-to-one name="dept" class="Dept" constrained="true"></one-to-one>
14             <!--  constrained="true" 表示Emp表中的主键同时作为外键参照Emp表中的主键 -->
15         </class>      
16     </hibernate-mapping>

View Code

Dept的配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5     <hibernate-mapping package="cn.rm.onetoone_fk">
 6         <class name="Dept" table="DEPT2016fk">
 7             <id name="deptid" column="DEPTID" type="int">
 8                 <generator class="sequence">
 9                     <param name="sequence">hb_ids</param>
10                 </generator>
11             </id>
12             <property name="mystreet" column="MYSTREET" type="string"></property>
13             <one-to-one name="emp" class="Emp" cascade="all" ></one-to-one>
14         </class>
15     </hibernate-mapping>

View Code

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