Hibernate多对一

通过many-to-one元素,可以定义一种常见的与另一个持久化类的关联。 这种关系模型是多对一关联（实际上是一个对象引用－译注）：这个表的一个外键引用目标表的 主键字段。

 

 One:

package org.hibernate.domain;

public class Department {
	private int id;
	private String name;

	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;
	}

	@Override
	public String toString() {
		return "Department [id=" + id + ", name=" + name + "]";
	}

}

 

Many:

package org.hibernate.domain;

public class Employee {
	private int id;
	private String name;
	private 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;
	}

	public Department getDepartment() {
		return department;
	}

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

	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", department="
				+ department + "]";
	}

}

 

映射文件：

<?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="org.hibernate.domain">
	<class name="Department" table="department">
		<id name="id">
			<generator class="native" />
		</id>

		<property name="name" />
	</class>
</hibernate-mapping>

 

<?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="org.hibernate.domain">
	<class name="Employee" table="employee">
		<id name="id">
			<generator class="native" />
		</id>

		<property name="name" />
		<!-- 如果忽略了column这个属性那么默认的外键与实体的属性一致 -->
		<many-to-one name="department" column="department_id" />
	</class>
</hibernate-mapping>

 

测试类：

package org.hibernate.test;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.domain.Department;
import org.hibernate.domain.Employee;
import org.hibernate.util.HibernateUtil;

public class ManyToOne {
	public static void main(String[] args) {
		Department department = add();
		System.out.println("add : " + department);
		System.out.println();
		department = queryDepartmentByDepartmentId(department.getId());
		System.out.println("queryDepartmentByDepartmentId : " + department);
		System.out.println();
		Employee employee = queryEmployeeByDepartmentId(department.getId());
		System.out.println("queryEmployeeByDepartmentId : " + employee);
	}

	public static Department add() {
		Session session = null;
		Transaction tx = null;

		try {
			Department department = new Department();
			department.setName("department name");

			Employee employee = new Employee();
			employee.setDepartment(department);// 对象模型：建立两个对象的关联
			employee.setName("employee name");

			session = HibernateUtil.getSession();
			tx = session.beginTransaction();
			session.save(department);
			session.save(employee);
			tx.commit();
			return department;
		} finally {
			if (session != null)
				session.close();
		}
	}

	public static Department queryDepartmentByDepartmentId(int departmentId) {
		Session s = null;
		Transaction tx = null;
		try {
			s = HibernateUtil.getSession();
			tx = s.beginTransaction();
			Department department = (Department) s.get(Department.class,
					departmentId);
			tx.commit();
			return department;
		} finally {
			if (s != null)
				s.close();
		}
	}

	public static Employee queryEmployeeByDepartmentId(int departmentId) {
		Session s = null;
		Transaction tx = null;
		try {
			s = HibernateUtil.getSession();
			tx = s.beginTransaction();
			Employee employee = (Employee) s.get(Employee.class, departmentId);
			Hibernate.initialize(employee.getDepartment());
			tx.commit();
			return employee;
		} finally {
			if (s != null)
				s.close();
		}
	}

}

 

控制台打印结果：