public class Team { private String id; private String name; private Set students=new HashSet(); } public class Course { private String id; private String name; private Set<Student> students; } public class Student { private String id; private String cardId; private int age; private String name; private Set<Course> courses; }
映射文件:
[b]Team.hbm.xml[/b] <hibernate-mapping package="hql"> <class name="Team" table="team"> <id name="id" column="id" type="string"> <generator class="uuid"></generator> </id> <property name="name" column="teamName" type="string"/> <set name="students" inverse="true" fetch="select" lazy="true"> <key column="team_id"/> <one-to-many class="Student"/> </set> </class> </hibernate-mapping> [b]Course.hbm.xml[/b] <hibernate-mapping package="hql"> <class name="Course" table="course"> <id name="id" column="id" type="string"> <generator class="uuid"></generator> </id> <property name="name" column="course_Name" type="string"/> <set name="students" inverse="true" fetch="select" lazy="true"> <key column="course_id"/> <many-to-many class="Student" column="student_id"/> </set> </class> </hibernate-mapping> [b]Student.hbm.xml[/b] <hibernate-mapping package="hql"> <class name="Student" table="student"> <id name="id" column="id" type="string"> <generator class="uuid"></generator> </id> <property name="name" column="student_Name" type="string"/> <set name="courses" inverse="true" fetch="select" lazy="true"> <key column="student_id"/> <many-to-many class="Course" column="course_id"/> </set> <many-to-one name="team" fetch="select" column="team_id" class="Team"/> </class> </hibernate-mapping>
SQL插入语句: create table course ( id varchar2(32) default '' not null , course_name varchar2(45) default null, primary key (id) ); create table team( id varchar2(32) default '' not null, team_name varchar2(45), primary key(id) ); create table student( id varchar2(32) default '' not null, student_name varchar2(45) , student_age number(10) , student_cardid varchar2(15) , team_id varchar2(32) , primary key(id) ); create table student_course( student_id varchar2(32) not null, course_id varchar2(32) not null ); alter table student_course add constraint FK_dk062403lt7507oncwn9uo4ro foreign key (course_id) references course; alter table student_course add constraint FK_3shg469d7jsf2a81b5x62jlq1 foreign key (student_id) references student; alter table student add constraint FK_8eu2c4tg0i8amuwx6n6d4i8h0 foreign key (team_id) references team(id); insert into student values ('1','alleni',22,'111',null); insert into student values ('2','eline',23,'222',null); insert into student values ('3','doudou',8,'333',null); insert into course values('111','Chinese'); insert into course values('222','Math'); insert into course values('333','English'); insert into course values('444','Physical'); insert into course values('555','Chemistry'); insert into course values('666','Geography'); insert into team values('team_a','drawer'); insert into team values('team_b','hunter'); update student set team_id ='team_a' where id='1'; update student set team_id ='team_a' where id='2'; update student set team_id ='team_b' where id='3'; insert into student_course values ('1','333'); insert into student_course values ('1','666'); insert into student_course values ('2','222'); insert into student_course values ('2','333'); insert into student_course values ('2','444'); insert into student_course values ('2','555'); insert into student_course values ('3','111'); insert into student_course values ('3','444'); insert into student_course values ('3','555');
=======================================================
HQL查询
方法1. 获取Object[]
/**
* Return the query results as a <tt>List</tt>. If the query contains
* multiple results pre row, the results are returned in an instance
* of <tt>Object[]</tt>.
*
* @return the result list
* @throws HibernateException
*/
public List list() throws HibernateException;
list方法可以返回一个Object[]类型对象,比如我们查询"select s.name,s.age from Student s",就会得到一个Object[]对象,如下所示:
name age
xx xx
xx xx
这里的每一行都是一个Object数组。因此我们可以通过强制类型转换,将其转换为Object[]。在这里其中[0]就是name,[1]就是age。 代码如下:
Query query=session.createQuery("select s.name,s.age from Student s"); List list=query.list(); for(int i=0;i<list.size();i++){ Object[] obj=(Object[]) list.get(i); System.out.println(obj[0]+", "+obj[1]); //输出结果:alleni, 22 // eline, 23 // doudou, 8 }
方法2.获取实例对象查询
//这种方式将返回的离散的值作为一个Student类型对象传了回来。 Query query=session.createQuery("select new Student(s.name,s.age) from Student s"); List<Student> list=query.list(); for(Student s:list){ System.out.println(s.getAge()); //有值 System.out.println(s.getName()); //有值 System.out.println(s.getCardId()); //null }
这种方式适用于当我们只需要部分值的时候。
上面的例子就通过包含部分元素(name,age)的Student的构造函数来获取Student实例。
这里只查询了age和name。 而其它元素都是空的。
注意: 这里必须在Student类中声明一个构造函数:
//这里的参数顺序必须和HQL语句中的new Student(s.name,s.age)一致。 public Student(String name,int age ) { this.age = age; this.name = name; }
没有这个构造函数,就会抛出异常(could not locate appropriate constructor)
方法3. 通过inner join进行查询
什么是内连接(inner join)?
select * from team join student on team.id=student.team_id where team.id='team_a';
也就是查询出Student表中team id=team_a的。等价于:
select * from team,student where team.id=student.team_id ; team.id='team_a';
(瞎写的,这里我也不会写)
具体代码实例:
Session session=HibernateUtil.openSession(); //Team中有students,这里用Team和Student进行一个内连接查询 //这里就不再遵循映射配置的lazy,直接从两个表中获取查询的数据了。 Query query=session.createQuery("from Team t join t.students"); List list=query.list(); System.out.println(list.size()); session.close(); for(int i=0;i<list.size();i++){ //这里获取的数组,[0]是Team, [1]是Student Object[] obj=(Object[]) list.get(i); Team team=(Team) obj[0]; Student student=(Student)obj[1]; System.out.println(team.getName()+" : "+student.getName() ); System.out.println(student.getCourses().iterator().next()); //course的内容并没有通过HQL语句中查询,所以这里会报错no Session //System.out.println(obj[0]+", "+obj[1]); }
输出结果为:
drawer : alleni
drawer : eline
hunter : doudou
可以看出Hibernate将inner join查询到的内容通过HQL语句格式,分别放入查询表所映射的类对象实例中。
方法4.通过实例对象进行查询
Session session=HibernateUtil.openSession(); Team team=(Team)session.load(Team.class,"team_a"); System.out.println(team.getName()); Query query=session.createQuery("from Student s where s.team=:team and s.age >20" ); query.setEntity("team", team); //通过setEntity高速Hibernate where s.team=:team这里team对应的实例。 List list=query.list(); System.out.println(list.size()); //2 System.out.println(((Student)list.get(0)).getName());//alleni System.out.println(((Student)list.get(1)).getName()); //eline
方法5.通过条件过滤器进行查询
Session session=HibernateUtil.openSession(); Team team=(Team)session.load(Team.class,"team_a"); System.out.println(team.getName()); Query query=session.createFilter(team.getStudents(), "where age>20"); List list=query.list(); System.out.println(list.size()); System.out.println(((Student)list.get(0)).getName()); System.out.println(((Student)list.get(1)).getName());
这里通过过滤器查询, 查询结果和方法4的一样。