hibernate多对一关联映射

知识点：
【

多对一(Employee - Department)
映射文件<many-to-one name=”depart” column=”depart_id”/>
column=”depart_id”与Employee外键对应 默认于Department主键对应
也可以通过property-ref来指定引用那个属性与外键对应

一对多(Department-Employee)
//映射集合
<set name=”employees”>
//指定查询根据depart_id去Employee查询
<key column=”depart_id”/>
<one-to-many class=”Employee”/>
</set>

】
照样看例子：

第一步搭建hibernate环境和先关配置文件件hibernate环境搭建

第二步：编写Employee  Department 实体类

Department.java:

public class Department {

private int id;
private String name;
private Set<Employee> employees;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Set<Employee> getEmployees() {
return employees;
}

public void setEmployees(Set<Employee> employees) {
this.employees = employees;
}

}

Employee.java:

public class Employee {

private int id;
private String name;
private Department department;

public Department getDepartment() {
return department;
}

public void setDepartment(Department department) {
this.department = department;
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

}

第三步：编写类的映射文件 分别为：配置文件命名规则见上面博客

Department.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.liyong.domain">

<class name="Department">
<!-- 生成主键 以natvie 自增长-->
<id name="id">
<generator class="native" />
</id>
<property name="name" />
<set name="employees">
<key column="department_id"/>
<one-to-many class="com.liyong.domain.Employee"/>
</set>
</class>

</hibernate-mapping>

Employee.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.liyong.domain">

<class name="Employee">
<!-- 生成主键 以natvie 自增长-->
<id name="id">
<generator class="native" />
</id>
<property name="name" />
<!--与department属性进行映射column指定这个外键的名称 这里是默认情况下
通过反射机制得到department属性的类然后通过这个类的属性文件与department类主键
于这个Employee外键进行映射，也可以通过property-ref来指定于这个外键对应的映射主键
是department那个属性一般都不会使用这个property-ref="name"则这个表的外键是department类中name属性
-->
<many-to-one name="department" column="department_id" />
</class>

</hibernate-mapping>

第四步：编写测试类

public class Test {

/**
* @param args
*/
public static void main(String[] args) {

//ManyToOneAdd();

//ManyToOnd
// Employee employee=ManyToOneQuery(1);
// //这里因为对代理对象进行了初始所有可以在这里得到引用对象
// System.out.println("name:"+employee.getDepartment().getName());


//OneToMany
Department department=QueryDepartment(1);
System.out.println("department length:"+department.getEmployees().size());
}

public static void ManyToOneAdd()
{
Session session=null;
Transaction transaction=null;

Department department=new Department();
department.setName("学生部");

Employee employee1=new Employee();
employee1.setName("张三");
employee1.setDepartment(department);

Employee employee=new Employee();
employee.setName("李勇");
employee.setDepartment(department);
try {

session = HibernateUtil.getSession();
transaction=session.beginTransaction();

session.save(department);
session.save(employee);
session.save(employee1);

transaction.commit();
} catch (Exception e) {

if(session!=null)
{
session.close();
}
}
}
//many-to-on
public static Employee QueryEmployee(int id)
{
Session session=null;
Transaction transaction=null;
Employee employee=null;
try {

session = HibernateUtil.getSession();
transaction=session.beginTransaction();
//这里得到是一个代理对象
employee=(Employee)session.get(Employee.class, id);
System.out.println(employee);
String name=employee.getDepartment().getName();
//初始化代理对象
Hibernate.initialize(employee);
//System.out.println("name:"+name);
transaction.commit();
} catch (Exception e) {

if(session!=null)
{
session.close();
}
return null;
}
return employee;
}
//one-to-many
public static Department QueryDepartment(int id)

{
Session session=null;
Transaction transaction=null;
Department department=null;
try {

session = HibernateUtil.getSession();
transaction=session.beginTransaction();

//下面这种查询只能通过Id查询
department=(Department)session.get(Department.class, id);

Hibernate.initialize(department);
transaction.commit();
} catch (Exception e) {

if(session!=null)
{
session.close();
}
return null;
}
return department;
}
}

第五步：测试....

源码见附件：