Question

以下示例工作正常，我希望您检查这是否是一个好方法，因为我之前没有这样的要求，我很好奇应该如何完成。

我有三个表：EMPLOYEE，MEETING，EMPLOYEE_MEETING以及EMPLOYEE和MEETING之间的MANY-TO-MANY关系只有两个映射。看来我能够插入，加载和更新所有内容。我想要实现的不是为关系创建额外的映射，DAO和单独的模型。

CREATE TABLE "employee_meeting" (
  "employee_id" bigint(20) NOT NULL,
  "meeting_id" bigint(20) NOT NULL,
  "opinion" varchar(50) DEFAULT NULL,
  PRIMARY KEY ("employee_id","meeting_id"),
 KEY "FK_MEETING" ("meeting_id"),
CONSTRAINT "FK_EMPLOYEE" FOREIGN KEY ("employee_id") REFERENCES "employee"      ("employee_id"),
 CONSTRAINT "FK_MEETING" FOREIGN KEY ("meeting_id") REFERENCES "meeting" ("meeting_id")
) ENGINE=InnoDB DEFAULT CHARSET=latin1$$


<hibernate-mapping package="net.viralpatel.hibernate">

<class name="Employee" table="EMPLOYEE">
    <id name="employeeId" column="EMPLOYEE_ID">
        <generator class="native" />
    </id>

    <property name="firstname" />
    <property name="lastname" column="lastname" />


<set name="meetings" table="EMPLOYEE_MEETING" inverse="false" lazy="false" fetch="select" cascade="all" >
    <key column="EMPLOYEE_ID" />
    <composite-element class="EmployeeMeeting">
        <parent name="employee" />
        <many-to-one name="meeting" column="MEETING_ID" not-null="true" cascade="all"
            class="Meeting" />
        <property name="opinion" column="OPINION" />
    </composite-element>
</set> 


</class>

<class name="Meeting" table="MEETING">

    <id name="meetingId" type="java.lang.Long"
        column="MEETING_ID">
        <generator class="native" />
    </id>

    <property name="subject" column="SUBJECT" />
    <property name="meetingDate" type="date" column="MEETING_DATE" />


</class>

 public static void main(String[] args) {

    SessionFactory sf = HibernateUtil.getSessionFactory();
    Session session = sf.openSession();
    session.beginTransaction();

    Meeting meeting1 = new Meeting("Quaterly Sales meeting");
    Meeting meeting2 = new Meeting("Weekly Status meeting");

    Employee employee1 = new Employee("Sergey", "Brin");
    Employee employee2 = new Employee("Larry", "Page");

    session.save(meeting1);

    EmployeeMeeting em = new EmployeeMeeting(employee1, meeting1, "BAD");

    employee1.getMeetings().add(em);

    session.save(employee1);
    session.save(employee2);

    session.getTransaction().commit();

    session.evict(employee1);
    session.beginTransaction();

    Employee e1 = (Employee) session.load(Employee.class, employee1.getEmployeeId());

    EmployeeMeeting em2 = e1.getMeetings().iterator().next();
    System.out.println("Test1:" + em2.getOpinion());

    em2.setOpinion("BETTER");
    session.save(e1);

    session.getTransaction().commit();

    session.evict(e1);
    session.beginTransaction();

    Employee e2 = (Employee) session.load(Employee.class, employee1.getEmployeeId());

    System.out.println("Test2:" + e2.getMeetings().iterator().next().getOpinion());
    System.out.println("Test2:" + e2.getMeetings().iterator().next().getMeeting().getMeetingId());
    System.out.println("Test2:" + e2.getMeetings().iterator().next().getEmployee().getEmployeeId());
     [/code]

Answer 1

以这种方式减少Manty-to-Many集合，没有双向，等于OneToMany集合。

我建议尊重多对多集合，在Meeting类下创建Employee数组并定义双向映射。

使用什么版本的hibernate？

Answer 2

从会议课程中我不需要接待员工..我只需要从员工级别访问会议 - 让员工需要插入，更新，删除会议。

我做了一些测试，似乎工作正常。一个奇怪的事情是当我运行这段代码时 - 我只是从数据库加载数据：

Employee e2 = (Employee) session.load(Employee.class, new Long(18));
    Employee e = (Employee) session.load(Employee.class, new Long(17));
    Iterator i = e.getMeetings().iterator();
    while (i.hasNext()){
        System.out.println(((EmployeeMeeting) i.next()).getMeeting().getMeetingId());
    }
    System.out.println(e2.getMeetings().iterator().next().getMeeting().getMeetingId());

    session.getTransaction().commit();
    session.close();

为什么HIbernate在我只从数据库加载数据时删除和插入会议

 Hibernate: select employee0_.EMPLOYEE_ID as EMPLOYEE1_0_0_, employee0_.firstname as     firstname0_0_, employee0_.lastname as lastname0_0_ from EMPLOYEE employee0_ where     employee0_.EMPLOYEE_ID=?
 Hibernate: select meetings0_.EMPLOYEE_ID as EMPLOYEE1_0_, meetings0_.MEETING_ID as      MEETING2_0_, meetings0_.OPINION as OPINION0_ from EMPLOYEE_MEETING meetings0_           where meetings0_.EMPLOYEE_ID=?
 Hibernate: select employee0_.EMPLOYEE_ID as EMPLOYEE1_0_0_, employee0_.firstname as firstname0_0_, employee0_.lastname as lastname0_0_ from EMPLOYEE employee0_ where employee0_.EMPLOYEE_ID=?
 Hibernate: select meetings0_.EMPLOYEE_ID as EMPLOYEE1_0_, meetings0_.MEETING_ID as MEETING2_0_, meetings0_.OPINION as OPINION0_ from EMPLOYEE_MEETING meetings0_ where meetings0_.EMPLOYEE_ID=?
12
11
7
13
7
Hibernate: delete from EMPLOYEE_MEETING where EMPLOYEE_ID=? and MEETING_ID=?
Hibernate: insert into EMPLOYEE_MEETING (EMPLOYEE_ID, MEETING_ID, OPINION) values (?, ?, ?)
Hibernate: delete from EMPLOYEE_MEETING where EMPLOYEE_ID=? and MEETING_ID=?
Hibernate: delete from EMPLOYEE_MEETING where EMPLOYEE_ID=? and MEETING_ID=?
Hibernate: delete from EMPLOYEE_MEETING where EMPLOYEE_ID=? and MEETING_ID=?
Hibernate: delete from EMPLOYEE_MEETING where EMPLOYEE_ID=? and MEETING_ID=?
Hibernate: insert into EMPLOYEE_MEETING (EMPLOYEE_ID, MEETING_ID, OPINION) values (?,   ?, ?)
Hibernate: insert into EMPLOYEE_MEETING (EMPLOYEE_ID, MEETING_ID, OPINION) values (?, ?, ?)
Hibernate: insert into EMPLOYEE_MEETING (EMPLOYEE_ID, MEETING_ID, OPINION) values (?, ?, ?)
Hibernate: insert into EMPLOYEE_MEETING (EMPLOYEE_ID, MEETING_ID, OPINION) values (?, ?, ?)

具有附加属性的多对多，并且没有将多对多映射为单独的实体

2 个答案: