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