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
public class Dept implements java.io.Serializable {
// Fields
private Integer deptId;
private String deptName;
private Set<Emp> emps=new HashSet<Emp>();
// Constructors
/** default constructor */
public Dept() {
}
/** full constructor */
public Dept(String deptName) {
this.deptName = deptName;
}
// Property accessors
public Integer getDeptId() {
return this.deptId;
}
public void setDeptId(Integer deptId) {
this.deptId = deptId;
}
public String getDeptName() {
return this.deptName;
}
public void setDeptName(String deptName) {
this.deptName = deptName;
}
public Set<Emp> getEmps() {
return emps;
}
public void setEmps(Set<Emp> emps) {
this.emps = emps;
}
}
Emp.java类
public class Emp implements java.io.Serializable {
// Fields
private Integer empNo;
private String empName;
private Date empBrithday;
private Dept dept;
// Constructors
/** default constructor */
public Emp() {
}
/** full constructor */
public Emp(String empName, Date empBrithday) {
this.empName = empName;
this.empBrithday = empBrithday;
}
// Property accessors
public Integer getEmpNo() {
return this.empNo;
}
public void setEmpNo(Integer empNo) {
this.empNo = empNo;
}
public String getEmpName() {
return this.empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public Date getEmpBrithday() {
return this.empBrithday;
}
public void setEmpBrithday(Date empBrithday) {
this.empBrithday = empBrithday;
}
public Dept getDept() {
return dept;
}
public void setDept(Dept dept) {
this.dept = dept;
}
}
Dept.hbm.xml
<hibernate-mapping>
<class name="com.db.entity.Dept" table="dept" catalog="mydb">
<id name="deptId" type="java.lang.Integer">
<column name="deptId" />
<generator class="native" />
</id>
<property name="deptName" type="java.lang.String">
<column name="deptName" length="32" />
</property>
<set name="emps" inverse="true" cascade="all">
<key column="deptId" not-null="true" />
<one-to-many class="com.db.entity.Emp" />
</set>
</class>
</hibernate-mapping>
Emp.hbm.xml
<hibernate-mapping>
<class name="com.db.entity.Emp" table="emp" catalog="mydb">
<id name="empNo" type="java.lang.Integer">
<column name="empNo" />
<generator class="native" />
</id>
<property name="empName" type="java.lang.String">
<column name="empName" length="20" />
</property>
<property name="empBrithday" type="java.util.Date">
<column name="empBrithday"/>
</property>
<many-to-one name="dept" column="deptId" class="com.db.entity.Dept" not-null="true" fetch="select" cascade="save-update,delete"/>
</class>
</hibernate-mapping>
hibernate.cfg.xml
<hibernate-configuration>
<session-factory>
<property name="dialect">
org.hibernate.dialect.MySQLDialect
</property>
<property name="connection.url">
jdbc:mysql://localhost:3306/mydb
</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<property name="connection.driver_class">
com.mysql.jdbc.Driver
</property>
<property name="myeclipse.connection.profile">
MyDBAccount
</property>
<mapping resource="com/db/entity/Dept.hbm.xml" />
<mapping resource="com/db/entity/Emp.hbm.xml" />
</session-factory>
</hibernate-configuration>
测试用例
public class TestOneMany {
public static void main(String[] args) throws ParseException {
// TODO Auto-generated method stub
Session session=HibernateSessionFactory.getSession();
Dept dept1=new Dept();
dept1.setDeptName("开发部");
Emp emp1=new Emp();
emp1.setEmpName("王洋");
String brithString="1999-03-05";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Date brithday=sdf.parse(brithString);
emp1.setEmpBrithday(brithday);
Emp emp2=new Emp();
emp2.setEmpName("李林");
brithString="2005-02-07";
brithday=sdf.parse(brithString);
emp2.setEmpBrithday(brithday);
//把emp和dpt分别添加到对方的实力对象中
dept1.getEmps().add(emp1);
dept1.getEmps().add(emp2);
emp1.setDept(dept1);
emp2.setDept(dept1);
session.beginTransaction();
session.save(dept1);
session.getTransaction().commit();
}
}
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 (?, ?, ?)