Hibernate映射set与List

1、对于set类型，如果集合中的元素是简单地类型，如字符串型，set使用另外一种映射方式：

team类：

 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;
     }
 }

映射文件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">

 <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">
             <key column="team_id"></key>
             <element column="name" type="string"></element>
         </set>
     </class>

 </hibernate-mapping>

使用set标签，一般要对应另外一张表，对于set元素是简单类型的，使用element子标签。

表的创建：

 create table student (team_id varchar(255) not null, name varchar(255))
 create table team (id varchar(255) not null, teamname varchar(255), primary key (id))
 alter table student add index FK8FFE823BB04F9E7 (team_id), add constraint FK8FFE823BB04F9E7 foreign key (team_id) references team (id)

测试类：

 import java.util.Map;

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

 public class HibernateTest
 {
     private static SessionFactory sessionFactory;

     static
     {
         try
         {
             sessionFactory = new Configuration().configure().buildSessionFactory();
         }
         catch(Exception ex)
         {
             ex.printStackTrace();
         }
     }

     public static void main(String[] args)
     {

         Session session = sessionFactory.openSession();
         Transaction tx = null;

         try
         {
             tx = session.beginTransaction();

             Team team = new Team();
             team.setTeamName("team");

             team.getStudents().add("zhangsan");
             team.getStudents().add("lisi");
             team.getStudents().add("wangwu");

             session.save(team);

             tx.commit();
         }
         catch(Exception ex)
         {
             if(null != tx)
             {
                 tx.rollback();
             }
             ex.printStackTrace();
         }
         finally
         {
             session.close();
         }
     }
 }

运行结果：

hibernate: insert into team (teamname, id) values (?, ?)
Hibernate: insert into student (team_id, name) values (?, ?)
Hibernate: insert into student (team_id, name) values (?, ?)
Hibernate: insert into student (team_id, name) values (?, ?)

map与set标签中的element子标签映射的是原子类型（String，date，int，long。。。），即能够直接映射到数据库表字段上的类型，而one-to-many映射的则是实体类型，指的是无法映射到表的某个字段，而是要映射到整张表的类型。

2、List的映射，list元素可以重复，而且是有顺序的。

举例：

 import java.util.ArrayList;
 import java.util.List;

 public class Team
 {
     private String id;

     private String teamName;

     private List students = new ArrayList();

     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 List getStudents()
     {
         return students;
     }

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

 }

 public class Student
 {
     private String id;

     private String cardId;

     private String name;

     private int age;

     private Team team;

     public String getId()
     {
         return id;
     }

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

     public String getCardId()
     {
         return cardId;
     }

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

     public String getName()
     {
         return name;
     }

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

     public int getAge()
     {
         return age;
     }

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

     public Team getTeam()
     {
         return team;
     }

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

 }

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>

         <list name="students" table="student" cascade="all">
             <key column="team_id"></key>
             <index column="index_"></index>
             <one-to-many class="com.cdtax.hibernate.Student"/>
         </list>
     </class>

 </hibernate-mapping>

对于Team，多了一个list标签，其中的子标签index来指出数据库表中的一列来维护list的顺序，因为list是有序的，而数据库中表是没有顺序的，只能用一个字段来维护。

 <?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="cardId" column="card_id" type="string"></property>
         <property name="name" column="name" type="string"></property>
         <property name="age" column="age" type="integer"></property>

         <many-to-one name="team" column="team_id" class="com.cdtax.hibernate.Team" cascade="none" fetch="join"></many-to-one>
     </class>
 </hibernate-mapping>

产生表的语句：

create table student (id varchar(255) not null, card_id varchar(255), name varchar(255), age integer, team_id varchar(255), index_ integer, primary key (id))
create table team (id varchar(255) not null, teamname varchar(255), primary key (id))

重点关注index_这一字段。

测试类：

 import java.util.Map;

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

 public class HibernateTest
 {
     private static SessionFactory sessionFactory;

     static
     {
         try
         {
             sessionFactory = new Configuration().configure().buildSessionFactory();
         }
         catch(Exception ex)
         {
             ex.printStackTrace();
         }
     }

     public static void main(String[] args)
     {

         Session session = sessionFactory.openSession();
         Transaction tx = null;

         try
         {
             tx = session.beginTransaction();

             Team team = new Team();
             team.setTeamName("team1");

             Team team2= new Team();
             team2.setTeamName("team2");

             Student s1 = new Student();
             Student s2 = new Student();
             Student s3 = new Student();
             Student s4 = new Student();
             Student s5 = new Student();
             Student s6 = new Student();

             s1.setName("zhangsan");
             s2.setName("lisi");
             s3.setName("wangwu");
             s4.setName("zhaoliu");
             s5.setName("5zhaoliu");
             s6.setName("6zhaoliu");

             team.getStudents().add(s1);
             team.getStudents().add(s2);

             team2.getStudents().add(s3);
             team2.getStudents().add(s4);
             team2.getStudents().add(s5);
             team2.getStudents().add(s6);

             session.save(team);
             session.save(team2);

             tx.commit();
         }
         catch(Exception ex)
         {
             if(null != tx)
             {
                 tx.rollback();
             }
             ex.printStackTrace();
         }
         finally
         {
             session.close();
         }
     }
 }

Hibernate: insert into team (teamname, id) values (?, ?)

Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into team (teamname, id) values (?, ?)
Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: insert into student (card_id, name, age, team_id, id) values (?, ?, ?, ?, ?)
Hibernate: update student set team_id=?, index_=? where id=?
Hibernate: update student set team_id=?, index_=? where id=?
Hibernate: update student set team_id=?, index_=? where id=?
Hibernate: update student set team_id=?, index_=? where id=?
Hibernate: update student set team_id=?, index_=? where id=?
Hibernate: update student set team_id=?, index_=? where id=?