Hibernate集合排序之内存排序

使用sort属性，我们可以通过在取回结果集后在内存中进行排序，然后返回一个经过排序的结果集合

数据库结构：

create table teamSort (id varchar(32),teamname varchar(32));
create table studentSort (name varchar(32),team_id varchar(32));
insert into teamSort values("1","team1");
insert into studentSort values("a","1");
insert into studentSort values("b","1");
insert into studentSort values("c","1");

pojo: student部分采用set集合，无实体类

package Collection.Sort;

import java.util.Set;

public class Team ...{
   private String id;
   private String teamname;
   private Set students;
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;
}

}

Team.hbm.xml

<?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">
<!-- 
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
<hibernate-mapping>
<class name="Collection.Sort.Team" table="teamSort" >
    <id name="id" unsaved-value="null">
      <generator class="uuid.hex"></generator>
    </id>
    <property name="teamname" type="string" column="teamname"></property>
    <!-- 以element内容升序返回 -->
    <set name="students" table="studentSort" cascade="all" sort="natural">
      <key column="team_id"></key>
      <element type="string" column="name"></element>
    </set>
</class>

</hibernate-mapping>

Hibernate.cfg.xml

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

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

<session-factory>
    <property name="connection.username">root</property>
    <property name="connection.url">
        jdbc:mysql://localhost:3306/schoolproject?characterEncoding=gb2312&amp;useUnicode=true
    </property>
    <property name="dialect">
        org.hibernate.dialect.MySQLDialect
    </property>
    <property name="myeclipse.connection.profile">mysql</property>
    <property name="connection.password">1234</property>
    <property name="connection.driver_class">
        com.mysql.jdbc.Driver
    </property>
    <property name="hibernate.dialect">
        org.hibernate.dialect.MySQLDialect
    </property>
    <property name="hibernate.show_sql">true</property>
    <property name="current_session_context_class">thread</property>
    <property name="jdbc.batch_size">15</property>
    <mapping resource="Collection/Sort/Team.hbm.xml" />




</session-factory>

</hibernate-configuration>

测试代码：

package Collection.Sort;


import java.io.File;
import java.util.Iterator;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class Test ...{


    public static void main(String[] args) ...{

        String filePath=System.getProperty("user.dir")+File.separator+"src/Collection/Sort"+File.separator+"hibernate.cfg.xml";
        File file=new File(filePath);
        System.out.println(filePath);
        SessionFactory sessionFactory=new Configuration().configure(file).buildSessionFactory();
        Session session=sessionFactory.openSession();
        Transaction t=session.beginTransaction();
        
        Team team=(Team)session.createQuery("from Team t where t.teamname='team1'").uniqueResult();
        Set result=team.getStudents();
        Iterator iter=result.iterator();
        while(iter.hasNext())...{
            System.out.println(iter.next());
        }
        
        t.commit();
        
    }

}

运行结果：

Hibernate: select team0_.id as id0_, team0_.teamname as teamname0_ from teamSort team0_ where team0_.teamname='team1'
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from studentSort students0_ where students0_.team_id=?
a
b
c

sort="natural"默认进行升序排列，如果我们想改成降序，则需要写一个类实现Comparator接口如下：

package Collection.Sort;

import java.util.Comparator;

public class Compare implements Comparator ...{

    public int compare(Object o1, Object o2) ...{
        String s1=(String)o1;
        String s2=(String)o2;
        if(s1.equals(s2))...{
            return 0;
        }
        else if(s1.compareTo(s2)>0)...{
            return -1;
        }
        else...{
            return 1;
        }
    
    }

}

然后更改Team.hbm.xml 配置sort属性

sort="Collection.Sort.Compare"

重新执行测试代码，结果如下：

Hibernate: select team0_.id as id0_, team0_.teamname as teamname0_ from teamSort team0_ where team0_.teamname='team1'
Hibernate: select students0_.team_id as team1_0_, students0_.name as name0_ from studentSort students0_ where students0_.team_id=?
c
b
a

注意：如果有Student实体类，并set中使用one-to-many或many-to-many标签，则比如使用sort="一个实现comparator接口的类"这样排序