现在的位置: 首页 > 综合 > 正文

12、Hibernate内存查询与数据库查询

2018年02月05日 ⁄ 综合 ⁄ 共 9809字 ⁄ 字号 小 中 大 ⁄ 评论关闭

set和map集合保存到数据库是无序的，但我们查询的时候希望带顺序查询，不是默认顺序，这就涉及查询排序问题。

有两种查询排序：内存排序及数据库排序

1、数据库排序使用order-by=“name asc”

对于map举例：

import java.util.HashMap;
import java.util.Map;

public class Team
{
	private String id;
	
	private String teamName;
	
	private Map students = new HashMap();

	public String getId()
	{
		return id;
	}

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

	public String getTeamName()
	{
		return teamName;
	}

	public void setTeamName(String teamName)
	{
		this.teamName = teamName;
	}

	public Map getStudents()
	{
		return students;
	}

	public void setStudents(Map students)
	{
		this.students = students;
	}
	
}

对应的hbm.xml映射文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	
	<class name="com.cdtax.hibernate.Team" table="team">
		
		<id name="id" column="id" type="string">
			<generator class="uuid">
			</generator>
		</id>
	
		
		
		<property name="teamName" column="teamname" type="string"></property>
		
		<map name="students" table="student" order-by="name asc"><!-- name是数据库字段 -->
			<key column="team_id"></key>
			<index column="name" type="java.lang.String"></index><!-- 指定Map中的key值 -->
			<element column="description" type="java.lang.String"></element><!-- 指定Map中的value值 -->
		</map>		 
	</class>
	
</hibernate-mapping>

一定要注意，这里的name是数据库字段的名字，而不是对象的成员变量名字。在进行sql查询时，会使用order by字句。

插入一些数据：

try
		{
			tx = session.beginTransaction();
			
			Team team = new Team();
			team.setTeamName("team 2");
			Map map = team.getStudents();
			map.put("lisi", "hello");
			map.put("zhangsan", "world");
			map.put("wangwu", "wangwu");
			map.put("eerr", "erere");
			session.save(team);
			
			
			
			tx.commit();
		}

插入数据库的数据student表：

team_id description name
402881c0424612810142461282370001 erere eerr
402881c0424612810142461282370001 hello lisi
402881c0424612810142461282370001 wangwu wangwu
402881c0424612810142461282370001 world zhangsan

查询：

try
		{
			tx = session.beginTransaction();
			
			
			Team team = (Team)session.createQuery("from Team t where t.teamName='team 2'").uniqueResult();
			
			Map map = team.getStudents();
			
			Collection col = map.values();
			
			Iterator iter = col.iterator();
			
			while(iter.hasNext())
			{
				System.out.println(iter.next());
			}
			
			tx.commit();
		}

执行结果：

Hibernate: select team0_.id as id0_, team0_.teamname as teamname0_ from team team0_ where team0_.teamname='team 2'
Hibernate: select students0_.team_id as team1_0_, students0_.description as descript2_0_, students0_.name as name0_ from student students0_ where students0_.team_id=? order by students0_.name asc
erere
hello
wangwu
world

注意：这里打印的结果是字段description，我们将order-by改为name desc：

执行结果：

Hibernate: select team0_.id as id0_, team0_.teamname as teamname0_ from team team0_ where team0_.teamname='team 2'
Hibernate: select students0_.team_id as team1_0_, students0_.description as descript2_0_, students0_.name as name0_ from student students0_ where students0_.team_id=? order by students0_.name desc
world
wangwu
hello
erere

对于set举例：

import java.util.HashSet;
import java.util.Set;

public class Team
{
	private String id;
	
	private String teamName;
	
	private Set students = new HashSet();

	public String getId()
	{
		return id;
	}

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

	public String getTeamName()
	{
		return teamName;
	}

	public void setTeamName(String teamName)
	{
		this.teamName = teamName;
	}

	public Set getStudents()
	{
		return students;
	}

	public void setStudents(Set students)
	{
		this.students = students;
	}
}

对应的映射文件、：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	
	<class name="com.cdtax.hibernate.Team" table="team">
		
		<id name="id" column="id" type="string">
			<generator class="uuid">
			</generator>
		</id>
			
		<property name="teamName" column="teamname" type="string"></property>
		
		<set name="students" table="student" order-by="name asc">
			<key column="team_id"></key>
			<element column="name" type="string"></element>
		</set>	 
	</class>
	
</hibernate-mapping>

插入测试数据：

try
		{
			tx = session.beginTransaction();
			
			Team team = new Team();
			team.setTeamName("team1");
			
			team.getStudents().add("zhangsan");
			team.getStudents().add("lisi");
			team.getStudents().add("wangwu");
			
			session.save(team);
			
			tx.commit();
		}

查询：

Hibernate: select team0_.id as id0_0_, team0_.teamname as teamname0_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from student students0_ where students0_.team_id=? order by students0_.name asc
lisi
wangwu
zhangsan

是有顺序的

如果将Team.hbm.xml的set修改一下，去掉order-by

<set name="students" table="student">
			<key column="team_id"></key>
			<element column="name" type="string"></element>
</set>

执行结果：

Hibernate: select team0_.id as id0_0_, team0_.teamname as teamname0_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from student students0_ where students0_.team_id=?
wangwu
lisi
zhangsan

2、内存排序使用sort属性

同上面的位置是一样的，就是order-by改为sort="" sort的属性值有三个：unsorted，不排序；natural，自然排序；第三个属性值是我们自己定义的排序规则类（Comparator接口）。

举例：将上例中Team.hbm.xml修改为：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	
	<class name="com.cdtax.hibernate.Team" table="team">
		
		<id name="id" column="id" type="string">
			<generator class="uuid">
			</generator>
		</id>
			
		<property name="teamName" column="teamname" type="string"></property>
		
		<set name="students" table="student" sort="unsorted">
			<key column="team_id"></key>
			<element column="name" type="string"></element>
		</set>	 
	</class>
	
</hibernate-mapping>

执行结果：

Hibernate: select team0_.id as id0_0_, team0_.teamname as teamname0_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from student students0_ where students0_.team_id=?
wangwu
lisi
zhangsan
改为

 sort="natural"

执行结果：

Hibernate: select team0_.id as id0_0_, team0_.teamname as teamname0_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from student students0_ where students0_.team_id=?
lisi
wangwu
zhangsan

可以看到按照字符的升序排列，而且sql查询语句也没有使用order by，这是查询出来后，在没有组装到对象前，由hibernate排序。

内存排序，我们自定义排序规则，方式是定义一个类，让其实现Comparator接口，并且实现该接口中的compare方法，在该方法中实现排序规则即可。然后将该自定义排序规则的类名作为sort的属性值即可。

测试：

import java.util.Set;

public class Team
{
	private String id;
	
	private String name;
	
	private Set<Student> students;

	public String getId()
	{
		return id;
	}

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

	public String getName()
	{
		return name;
	}

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

	public Set<Student> getStudents()
	{
		return students;
	}

	public void setStudents(Set<Student> students)
	{
		this.students = students;
	}
}

public class Student
{
	private String id;
	
	private String name;
	
	private String cardId;
	
	private int age;
	
	
	public String getCardId()
	{
		return cardId;
	}

	public void setCardId(String cardId)
	{
		this.cardId = cardId;
	}

	public int getAge()
	{
		return age;
	}

	public void setAge(int age)
	{
		this.age = age;
	}

	private Team team;

	public Team getTeam()
	{
		return team;
	}

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

	public String getId()
	{
		return id;
	}

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

	public String getName()
	{
		return name;
	}

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

}

对应的映射文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	
	<class name="com.cdtax.hibernate.Team" table="team">
		
		<id name="id" column="id" type="string">
			<generator class="uuid">
			</generator>
		</id>
	
		
		
		<property name="name" column="name" type="string"></property>
		
		<set name="students" lazy="false" cascade="all" inverse="true" fetch="select" sort="com.cdtax.hibernate.MyComparator">
			<key column="team_id"></key>
			<one-to-many class="com.cdtax.hibernate.Student"/>
		</set>

		 
	</class>
	
</hibernate-mapping>

注意sort的值为我们自定义的比较器类 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
	
	<class name="com.cdtax.hibernate.Student" table="student">
	
		<id name="id" column="id" type="string">
			<generator class="uuid"></generator>
		</id>
		
		<property name="name" column="name" type="string"></property>
		<property name="cardId" column="cardid" type="string"></property>
		<property name="age" column="age" type="integer"></property>
		
		<many-to-one name="team" class="com.cdtax.hibernate.Team" column="team_id" fetch="select" cascade="all"></many-to-one>
		
	</class>
</hibernate-mapping>

我们的比较器：

import java.util.Comparator;

public class MyComparator implements Comparator<Student>
{
	@Override
	public int compare(Student o1, Student o2)
	{
		if(o1 == o2)
		{
			return 0;
		}
		
		int result = o1.getCardId().compareTo(o2.getCardId());
		
		if(result != 0)
		{
			return result;
		}
		
		return o1.getName().compareTo(o2.getName());
	}
}

测试程序：

try
		{
			tx = session.beginTransaction();
			
			Team team1 = (Team)session.get(Team.class,"402881c04246244c014246244d920001");
			
			Set<Student> set = team1.getStudents();
			
			for(Iterator<Student> iter = set.iterator();iter.hasNext();)
			{
				System.out.println(iter.next().getName());
			}
			
			tx.commit();
		}

数据库数据：

id name team_id cardid age
402881c04246244c014246244d920003 lisi 402881c04246244c014246244d920001 aa 7
402881c04246244c014246244d920012 zhang 402881c04246244c014246244d920001 bc 9
402881c04246244c014246244d920013 wang 402881c04246244c014246244d920001 cs 54
402881c04246244c014246244d920015 zliu 402881c04246244c014246244d920001 cs 32
402881c04246244c014246244d920016 aaaaa 402881c04246244c014246244d920001 aa 32

执行结果

Hibernate: select team0_.id as id1_0_, team0_.name as name1_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team5_1_, students0_.id as id1_, students0_.id as id0_0_, students0_.name as name0_0_, students0_.cardid as cardid0_0_, students0_.age as age0_0_, students0_.team_id as team5_0_0_ from student students0_ where students0_.team_id=?
aaaaa
lisi
zhang
wang
zliu

如果我们需要相反的顺序，修改比较器类：

import java.util.Comparator;

public class MyComparator implements Comparator<Student>
{
	@Override
	public int compare(Student o1, Student o2)
	{
		if(o1 == o2)
		{
			return 0;
		}
		
		int result = o1.getCardId().compareTo(o2.getCardId());
		
		if(result != 0)
		{
			return -result;
		}
		
		return -o1.getName().compareTo(o2.getName());
	}
}

执行结果：

Hibernate: select team0_.id as id1_0_, team0_.name as name1_0_ from team team0_ where team0_.id=?
Hibernate: select students0_.team_id as team5_1_, students0_.id as id1_, students0_.id as id0_0_, students0_.name as name0_0_, students0_.cardid as cardid0_0_, students0_.age as age0_0_, students0_.team_id as team5_0_0_ from student students0_ where students0_.team_id=?
zliu
wang
zhang
lisi
aaaaa

返回
【上篇】
【下篇】

作者:

抱歉!评论已关闭.

返回首页

Copyright © 2013-2018 学步园  保留所有权利.
软文销售 QQ客服：2265327166 点击这里给我发消息（其他合作也可洽谈）
必威体育
必威电竞