Hibernate (9) _ many to one association map

This series of blog summarized here: Hibernate Summary

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Source project file: hibernate4.3_04

Many to one association mapping

Examples of the use of staff and team

Class Diagram:

Database Diagram:

1, to create a model

Create more end

package com.wyx.hiber.model;

import java.util.Date;

public class Emp
{

	private Integer empNo;

	private String ename;

	private Date birthday;

	private Integer gender;

	private String address;

	/**
	 * 引入一的一端的类作为成员，指定多对一的关系
	 * 
	 */
	private Team team;

	public Team getTeam()
	{
		return team;
	}

	public void setTeam(Team team)
	{
		this.team = team;
	}

	public Integer getEmpNo()
	{
		return empNo;
	}

	public void setEmpNo(Integer empNo)
	{
		this.empNo = empNo;
	}

	public String getEname()
	{
		return ename;
	}

	public void setEname(String ename)
	{
		this.ename = ename;
	}

	public Date getBirthday()
	{
		return birthday;
	}

	public void setBirthday(Date birthday)
	{
		this.birthday = birthday;
	}

	public Integer getGender()
	{
		return gender;
	}

	public void setGender(Integer gender)
	{
		this.gender = gender;
	}

	public String getAddress()
	{
		return address;
	}

	public void setAddress(String address)
	{
		this.address = address;
	}

	@Override
	public String toString()
	{
		return "Emp [empNo=" + empNo + ", ename=" + ename + ", birthday="
				+ birthday + ", gender=" + gender + ", address=" + address
				+ "]";
	}

}

Creating a end

package com.wyx.hiber.model;

public class Team
{

	private Integer tId;

	private String tName;

	private String loc;

	public Integer gettId()
	{
		return tId;
	}

	public void settId(Integer tId)
	{
		this.tId = tId;
	}

	public String gettName()
	{
		return tName;
	}

	public void settName(String tName)
	{
		this.tName = tName;
	}

	public String getLoc()
	{
		return loc;
	}

	public void setLoc(String loc)
	{
		this.loc = loc;
	}

	@Override
	public String toString()
	{
		return "Team [tId=" + tId + ", tName=" + tName + ", loc=" + loc + "]";
	}

}

2, configuration mapping file

Configure multiple end

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.wyx.hiber.model">
	<class name="Emp" table="t_emp">
		<id name="empNo" column="emp_no">
			<generator class="native"></generator>
		</id>
		<property name="ename"></property>
		<property name="birthday"></property>
		<property name="gender"></property>
		<property name="address"></property>
		<!-- 
			指定多对一的关系
			name：多的一端（emp）的类中的一的类（team）的属性名
			column:建表后多的一端（t_emp）中的外键
			cascade：delete切记不要使用
					save-update级联保存或更新
					all包含了以上两种
					none不使用级联（默认的）
		 -->
		<many-to-one name="team" column="t_id" cascade="save-update"></many-to-one>
	</class>
	
</hibernate-mapping>

A configuration of an end

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.wyx.hiber.model">
	<class name="Team" table="t_team">
		<id name="tId" column="t_id">
			<generator class="native"></generator>
		</id>
		<property name="tName" column="t_name"></property>
		<property name="loc"></property>
	</class>
</hibernate-mapping>

After you create the Hibernate mapping file you want to register to our hibernate.cfg.xml, and then export the database can be.

3, many-test

Storage

public void testAdd()
{
	Session session = HibernateUtils.getSession();
	Transaction tx = session.beginTransaction();

	try
	{
		// 创建一支球队
		Team t = new Team();
		t.settName("公牛");
		t.setLoc("芝加哥");
		// 保存球队
		session.save(t);

		// 创建员工
		Emp emp = new Emp();
		emp.setEname("乔丹");
		emp.setGender(1);
		emp.setBirthday(new Date());
		emp.setAddress("芝加哥");

		Emp emp1 = new Emp();
		emp1.setEname("菲尔");
		emp1.setGender(1);
		emp1.setBirthday(new Date());
		emp1.setAddress("芝加哥");
		// 设置员工和球队的关系
		emp.setTeam(t);
		emp1.setTeam(t);
		// 保存员工
		session.save(emp);
		session.save(emp1);
		tx.commit();
	} catch (Exception e)
	{
		e.printStackTrace();
		tx.rollback();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

Note: be sure to keep a hold of one end of the multi-end time, if one end is a transient object error will be

correct output



saved many to one relationship when you can also use cascading manner

using cascaded save there is no need to save a separate one of the end.

Inquire

Use get to query

@Test
public void testQuery()
{
	Session session = HibernateUtils.getSession();

	try
	{
		// 调用get方法来查询指定要查询的类和id
		Emp emp = (Emp) session.get(Emp.class, 5);
		System.out.println(emp);
		System.out.println(emp.getTeam());
	} catch (Exception e)
	{
		e.printStackTrace();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

Use load to query

@Test
public void testQuery1()
{
	Session session = HibernateUtils.getSession();

	try
	{
		// 调用load方法来查询指定要查询的类和id
		Emp emp = (Emp) session.load(Emp.class, 5);
		System.out.println(emp);
		System.out.println(emp.getTeam());
	} catch (Exception e)
	{
		e.printStackTrace();
	} finally
	{
		HibernateUtils.closeResource(session);
	}
}

If wrong, please correct me!