JPA关系映射之one-to-many和many-to-one

one-to-many（一对多）和many-to-one（多对一）双向关联

假设部门与员工是一对多关系，反过来员工与部门就是多对一关系。

Dept.java类

 1 public class Dept implements java.io.Serializable {
 2 
 3     // Fields
 4 
 5     private Integer deptId;
 6     private String deptName;
 7     private Set<Emp> emps=new HashSet<Emp>();
 8 
 9     // Constructors
10 
11     /** default constructor */
12     public Dept() {
13     }
14 
15     /** full constructor */
16     public Dept(String deptName) {
17         this.deptName = deptName;
18     }
19 
20     // Property accessors
21 
22     public Integer getDeptId() {
23         return this.deptId;
24     }
25 
26     public void setDeptId(Integer deptId) {
27         this.deptId = deptId;
28     }
29 
30     public String getDeptName() {
31         return this.deptName;
32     }
33 
34     public void setDeptName(String deptName) {
35         this.deptName = deptName;
36     }
37 
38     public Set<Emp> getEmps() {
39         return emps;
40     }
41 
42     public void setEmps(Set<Emp> emps) {
43         this.emps = emps;
44     }
45 
46 }

Emp.java类

 1 public class Emp implements java.io.Serializable {
 2 
 3     // Fields
 4 
 5     private Integer empNo;
 6     private String empName;
 7     private Date empBrithday;
 8     private Dept dept;
 9 
10     // Constructors
11 
12     /** default constructor */
13     public Emp() {
14     }
15 
16     /** full constructor */
17     public Emp(String empName, Date empBrithday) {
18         this.empName = empName;
19         this.empBrithday = empBrithday;
20     }
21 
22     // Property accessors
23 
24     public Integer getEmpNo() {
25         return this.empNo;
26     }
27 
28     public void setEmpNo(Integer empNo) {
29         this.empNo = empNo;
30     }
31 
32     public String getEmpName() {
33         return this.empName;
34     }
35 
36     public void setEmpName(String empName) {
37         this.empName = empName;
38     }
39 
40     public Date getEmpBrithday() {
41         return this.empBrithday;
42     }
43 
44     public void setEmpBrithday(Date empBrithday) {
45         this.empBrithday = empBrithday;
46     }
47 
48     public Dept getDept() {
49         return dept;
50     }
51 
52     public void setDept(Dept dept) {
53         this.dept = dept;
54     }
55 
56 }

Dept.hbm.xml

 1 <hibernate-mapping>
 2     <class name="com.db.entity.Dept" table="dept" catalog="mydb">
 3         <id name="deptId" type="java.lang.Integer">
 4             <column name="deptId" />
 5             <generator class="native" />
 6         </id>
 7         <property name="deptName" type="java.lang.String">
 8             <column name="deptName" length="32" />
 9         </property>
10         <set name="emps" inverse="true" cascade="all">
11             <key column="deptId" not-null="true" />
12             <one-to-many class="com.db.entity.Emp" />
13         </set>
14     </class>
15 </hibernate-mapping>

Emp.hbm.xml

 1 <hibernate-mapping>
 2     <class name="com.db.entity.Emp" table="emp" catalog="mydb">
 3         <id name="empNo" type="java.lang.Integer">
 4             <column name="empNo" />
 5             <generator class="native" />
 6         </id>
 7         <property name="empName" type="java.lang.String">
 8             <column name="empName" length="20" />
 9         </property>
10         <property name="empBrithday" type="java.util.Date">
11             <column name="empBrithday"/>
12         </property>
13         <many-to-one name="dept" column="deptId" class="com.db.entity.Dept" not-null="true"  fetch="select" cascade="save-update,delete"/>
14     </class>
15 </hibernate-mapping>

hibernate.cfg.xml

 1 <hibernate-configuration>
 2 
 3     <session-factory>
 4         <property name="dialect">
 5             org.hibernate.dialect.MySQLDialect
 6         </property>
 7         <property name="connection.url">
 8             jdbc:mysql://localhost:3306/mydb
 9         </property>
10         <property name="connection.username">root</property>
11         <property name="connection.password">123456</property>
12         <property name="connection.driver_class">
13             com.mysql.jdbc.Driver
14         </property>
15         <property name="myeclipse.connection.profile">
16             MyDBAccount
17         </property>
18         <mapping resource="com/db/entity/Dept.hbm.xml" />
19         <mapping resource="com/db/entity/Emp.hbm.xml" />
20     </session-factory>
21 
22 </hibernate-configuration>

测试用例

 1 public class TestOneMany {
 2 
 3     public static void main(String[] args) throws ParseException {
 4         // TODO Auto-generated method stub
 5 
 6         Session session=HibernateSessionFactory.getSession();
 7         Dept dept1=new Dept();
 8         dept1.setDeptName("开发部");
 9         Emp emp1=new Emp();
10         emp1.setEmpName("王洋");
11         String brithString="1999-03-05";
12         SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
13         Date brithday=sdf.parse(brithString);
14         emp1.setEmpBrithday(brithday);
15         Emp emp2=new Emp();
16         emp2.setEmpName("李林");
17         brithString="2005-02-07";
18         brithday=sdf.parse(brithString);
19         emp2.setEmpBrithday(brithday);
20         //把emp和dpt分别添加到对方的实力对象中
21         dept1.getEmps().add(emp1);
22         dept1.getEmps().add(emp2);
23         emp1.setDept(dept1);
24         emp2.setDept(dept1);
25         session.beginTransaction();
26         session.save(dept1);
27         session.getTransaction().commit();
28     }
29 
30 }

 注意：

在一的set配置中声明inverse=“true”，意味着Dept不在作为主控方，将关联关系的维护工作交给关联对象Emp来完成。在保存dept1对象的时不在关心Emp类中dept属性对应的deptId列，必须由Emp自己去维护，即设置emp.setDept(dept)  

上述操作完成的sql语句是：

Hibernate: insert into mydb.dept (deptName) values (?)
Hibernate: insert into mydb.emp (empName, empBrithday, deptId) values (?, ?, ?)
Hibernate: insert into mydb.emp (empName, empBrithday, deptId) values (?, ?, ?)

posted @ 2016-06-30 22:24  SaraMorning  阅读(4239)  评论(0)  编辑  收藏  举报