HIBERNATE一对多配置实例

HIBERNATE一对多配置实例
1．环境：假定班级和学生是一对多的关系，班级是一，学生是多，对应表格分别是：zlass ,student
2．创建Zlass和Student对象
//Zlass对象---------------------------------------------------------
    public class Zlass{

private String class_id;
private String class_name;
private java.util.Set students;

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

public void setClassName(String className){
    this.class_name = className;
}

public void setStudents(java.util.Set students){
    this.students = students;
}

public String getId(){
    return class_id;
}

public String getClassName(){
    return class_name;
}

public java.util.Set getStudents(){
    return students;
}

}

//学生对象
public class Student{
       private String student_id;
       private String name;
       private Address address;
       private java.util.Set events;
       private java.util.Set lessons;
       private Zlass zlass;

       public Zlass getZlass(){
              return zlass;
       }

       public String getStudentId(){
              return student_id;
       }

       public String getName(){
              return name;
       }

       public Address getAddress(){
              return address;
       }

       public java.util.Set getEvents(){
              return events;
       }

       public java.util.Set getLessons(){
              return lessons;
       }

       public void setZlass(Zlass zlass){
              this.zlass = zlass;
       }

       public void setStudentId(String studentId){
              this.student_id = studentId;
       }

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

       public void setAddress(Address address){
              this.address = address;
       }

       public void setEvents(java.util.Set events){
              this.events =events;
       }

       public void setLessons(java.util.Set lessons){
              this.lessons = lessons;
       }

}

//配置文件
//----------Zlass.hbm.xml---------------
<hibernate-mapping package="com.softWork.school">
<class name="Zlass" table="class">
    <id name="id" column="id" type="string" length="20">
      <generator class="assigned"/>
    </id>
    <property name="className" column="class_name" type="string" length="200"/>

    <set name="students" inverse="false" cascade="all">
      <key column="class_id"/>
      <one-to-many class="Student"/>
    </set>
</class>
</hibernate-mapping>
//-------------Student.hbm.xml---------------
<hibernate-mapping package="com.softWork.school">
<class name="Student" table="student">
    <id name="studentId" column="student_id" type="string" length="20">
      <generator class="assigned"/>
    </id>
    <property name="name" type="string" length="20"/>
    <component name="address" class="Address">
      <property name="state" column="state" type="string"></property>
      <property name="city" column="city" type="string"></property>
      <property name="street" column="street" type="string"></property>
    </component>
    <set name="events" inverse="false" cascade="all">
      <key column="student_id"></key>
      <one-to-many class="Event"></one-to-many>
    </set>

    <set name="lessons" table="student_lesson">
      <key column="student_id"/>
      <many-to-many class="Lesson" column="lesson_id" />
    </set>
    <many-to-one name="zlass" column="class_id" class="Zlass"/>
</class>
</hibernate-mapping>

以上使用的是班级一端维护关系，并级连操作

3．使用级连操作数据
1）新增班级
       Zlass zlass = new Zlass();
       zlass.setId("971002");
       zlass.setClassName("机制97-1班");
session.saveOrUpdate(zlass);
2）为班级新增学生
主动端操作：
      Zlass zlass = (Zlass)session.load(Zlass.class,"971002");
      Student student = new Student();
      student.setStudentId("005");
      student.setName("没名");
      zlass.getStudents().add(student);
      session.saveOrUpdate(zlass);
被动端操作：
      Zlass zlass = (Zlass)session.load(Zlass.class,"971002");
      Student student = new Student();
      student.setStudentId("006");
      student.setName("006");
      student.setZlass(zlass);
session.saveOrUpdate(student);
3）删除学生资料
主动端操作：
主动端除非删除自己，并设置了级连才能删除子对象，否则无法完成
//-----以下代码将只删除两者之间的关系，即将学生的class_id设置为null-----
Zlass zlass = (Zlass)session.load(Zlass.class,"971001");
java.util.Iterator iterator = zlass.getStudents().iterator();
      if (iterator.hasNext())
        zlass.getStudents().remove(iterator.next());
      session.saveOrUpdate(zlass);
被动端操作：
              Student student = (Student)session.load(Student.class,"002");
session.delete(student);
4）修改学生资料
通过班级修改学生资料

Zlass zlass = (Zlass)session.load(Zlass.class,"971002");
      java.util.Iterator iterator = zlass.getStudents().iterator();
      if (iterator.hasNext()){
        Student student = (Student)iterator.next();
        student.setName("名字已修改");
      }
session.saveOrUpdate(zlass);

读取返回的Set型数据：
java.util.Set set = student.getEvents();
java.util.Iterator iterator = set.iterator();
while(iterator.hasNext()){
evt = (Event)iterator.next();
System.out.println(evt.getContent());
System.out.println(evt.getDate().toString());
}

4．注意：
如果需要从多放引导到一方，需要在一方配置文件中设置inverse=”true”参数，以设定一方到多方的设定是逆向映射，对关联的逆向端所做的修改将不会被持久化。
Inverse=”true”的表示两个实体的关系由对方去维护。
5．推荐配置，一般的将”一”这一端设置为inverse=”false”，cascade=”all” ，这样一般的操作只需要在”一”这一端操作,此适合于标志性一对多的情况，如销售单和销售明细
如果是非标志性一对多，则一般的将inverse=”false”,cascade=”none”,这样关系永远在主动一端进行控制
示范：假如A对B是一对多，当A中原来有B1，B2，B3，当A中的集合中只包含B1，B2时，那么B中B3的外码将被设置为NULL，这个是CASCADE=“FALSE”的情况下的结果

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