多对一映射与一对多映射：
使用部门和员工的关系来说明问题.一个部门可以有多个员工,但是一个员工只属于一个部门.
开发步骤：
(1)JavaBean的设计,Dept(部门表) Employee(员工表)
(2)映射关系
(3)测试
1.Dept和Employee Javabean
Dept
package cn.itcast.one2many;import java.util.HashSet;import java.util.Set;public class Dept {private int deptId;private String deptName;private Set<Employee> emps=new HashSet<Employee>();public int getDeptId() {return deptId;}public void setDeptId(int deptId) {this.deptId = deptId;}public String getDeptName() {return deptName;}public void setDeptName(String deptName) {this.deptName = deptName;}public Set<Employee> getEmps() {return emps;}public void setEmps(Set<Employee> emps) {this.emps = emps;}}Employee
package cn.itcast.one2many;public class Employee {private int empId;private String empName;private Dept dept;public int getEmpId() {return empId;}public void setEmpId(int empId) {this.empId = empId;}public String getEmpName() {return empName;}public void setEmpName(String empName) {this.empName = empName;}public Dept getDept() {return dept;}public void setDept(Dept dept) {this.dept = dept;}}2.映射文件
Dept.hbm.xml
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"""><hibernate-mapping package="cn.itcast.one2many" auto-import="true"><class name="Dept" table="t_dept"><id name="deptId"><generator class="native"></generator></id><property name="deptName" column="deptName" length="20" type="string"></property><span style="color:#ff0000;"><!–一对多的关系dept映射关键点1.指定映射的集合属性2.集合属性对应的集合表3.集合表的外键字段 "dept_id"4.集合元素的类型Set<>尖括号里面的 –></span> <set name="emps" table="t_employee"><key column="dept_id"></key><one-to-many class="Employee"/> </set></class></hibernate-mapping>Employee.hbm.xml
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"""><hibernate-mapping package="cn.itcast.one2many" auto-import="true"><class name="Employee" table="t_employee"><id name="empId"><generator class="native"></generator></id><property name="empName" column="empName" length="20" type="string"></property><span style="color:#ff0000;"><!–多对一：1.映射的部门属性：dept2.映射部门的属性,对应的外键字段3.部门的类型 –></span><many-to-one name="dept" column="dep_id" class="Dept"></many-to-one></class></hibernate-mapping>3.测试类
package cn.itcast.one2many;import org.hibernate.Transaction;import org.hibernate.classic.Session;import org.junit.Test;import cn.itcast.utils.HibernateUtil;public class App {@Testpublic void testOne2Many(){Session session = HibernateUtil.getSession();Transaction transaction = session.beginTransaction();//通过部门维护员工//1.部门Dept dept=new Dept();dept.setDeptName("行政部");//2.员工Employee emp_lwk=new Employee();emp_lwk.setEmpName("李卫康");Employee emp_hw=new Employee();emp_hw.setEmpName("韩玮");//3.关系dept.getEmps().add(emp_lwk);dept.getEmps().add(emp_hw);//4.保存到数据库要保存每一个对象session.save(emp_hw);session.save(emp_lwk);session.save(dept);transaction.commit();session.close();}}运行测试可以发现数据库中的表数据：
最重要的是今天的心。
