12、Hibernate内存查询与数据库查询

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