Hibernate学习16 -- 关联映射6 -- 多对多关联2 -- 多对多关联双向

 

l         题目：课程和老师是多对多关系：T_COURSE(CID,CNAME)，T_TEACHER(TID,TNAME)。要求利用hibernate，实现：对课程的信息进行查询的时候，无需另外查询就可以得到老师的信息，对老师信息查询的时候也能知道他教了哪些课程

l         首先建立第三个表：T_JIAOKE(TID,CID)

l         步骤：

n         建立POJO:Course.java，Teacher.java，建立hibernate的配置文件，将两个hbm文件与其绑定

n         在Course.java里面建立一个Set类型的属性，准备装老师；在Teacher.java里面建立一个Set类型属性，准备装课程

n         在两个hbm文件中增加：

<set name=”set属性名称” table=”第三个对应的表名称” lazy=”false” inverse=”false” >     <key column=”本表在第三个对应表外键”/>    <many-to-many        class=”另一表对应的类”        column=”另一个在第三个表中对应的外键”    /> </set>

l         代码实现：

Course.java

package po;   import java.util.Set;   public class Course {        private String cid;        private String cname;        private Set teachers;        public Set getTeachers() {               return teachers;        }        public void setTeachers(Set teachers) {               this.teachers = teachers;        }        public String getCid() {               return cid;        }        public void setCid(String cid) {               this.cid = cid;        }        public String getCname() {               return cname;        }        public void setCname(String cname) {               this.cname = cname;        }   }

Teacher.java

package po;   import java.util.Set;   public class Teacher {        private String tid;        private String tname;        private Set courses;        public String getTid() {               return tid;        }        public void setTid(String tid) {               this.tid = tid;        }        public String getTname() {               return tname;        }        public void setTname(String tname) {               this.tname = tname;        }        public Set getCourses() {               return courses;        }        public void setCourses(Set courses) {               this.courses = courses;        } }

Course.hbm.xml

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping>        <class name="po.Course" table="T_COURSE">                <id name="cid" column="CID">                        <generator class="assigned"/>                                  </id>               <property name="cname"      column="CNAME"/>               <set               name="teachers"               table="T_JIAOKE"               lazy="false"               inverse="false"               >               <key column="CID" ></key>               <many-to-many                      class="po.Teacher"                      column="TID"               />                  </set>                   </class> </hibernate-mapping>

Teacher.hbm.xml

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping>        <class name="po.Teacher" table="T_TEACHER">                    <id name="tid" column="TID">                         <generator class="assigned"/>                                  </id>               <property name="tname"       column="TNAME"/>                   <set               name="courses"               table="T_JIAOKE"               lazy="false"               inverse="false"               >               <key column="TID" ></key>               <many-to-many                      class="po.Course"                      column="CID"               /> </set>                                    </class>        </hibernate-mapping>

测试类：

package test; import java.util.Iterator; import java.util.Set;   import org.hibernate.Session;   import po.Course; import po.Teacher;     public class TestMany2Many {          public static void main(String[] args) {               Session session = util.HibernateSessionFactory.getSession();               //001老师教的课程               Teacher teacher = (Teacher)session.get(Teacher.class, "001");               System.out.println(teacher.getTname());               Set set = teacher.getCourses();               Iterator ite = set.iterator();               while(ite.hasNext()){                      Course course = (Course)ite.next();                      System.out.println(course.getCname());               }               util.HibernateSessionFactory.closeSession();//关闭                                    }   }