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