hibernate 多對多

0.0 參數(shù)

class.catalog="指定數(shù)據(jù)庫的鞋喇，建議刪掉"

set.inverse:是否要放棄維護外鍵關(guān)系
    true:  放棄維護主鍵
    false: 我
    default value:false
set.cascade:是否需要級聯(lián)操作 (5個)
      save-update：A保存侦香，同時保存B
      delete：刪除A鄙皇，同時刪除B伴逸，AB都不存在
      delete-orphan：孤兒刪除，解除關(guān)系颓芭，同時將B刪除亡问，A存在的州藕。
      如果需要配置多項酝陈，使用逗號分隔沉帮。<set cascade="save-update,delete">

      all : save-update 和 delete 整合
      all-delete-orphan : 三個整合

?   容器<set> 提供兩個屬性：fetch穆壕、lazy
    fetch：確定使用sql格式
    lazy：關(guān)聯(lián)對象是否延遲喇勋。
?   fetch：join、select压彭、subselect
    join：底層使用迫切左外連接
    select：使用多個select語句（默認(rèn)值）
    subselect：使用子查詢
?   lazy：false、true皱碘、extra
    false：立即
    true：延遲（默認(rèn)值）
    extra：極其懶惰

1.0 簡單多對多(雙向多對多)


<hibernate-mapping package="cc.sirius.bean">
    <class name="對應(yīng)類名" table="表名">
        <id name="主鍵">
            <generator class="主鍵生成策略"></generator>
        </id>
        <property name="類對象的對應(yīng)屬性"></property>
        <set name="對應(yīng)set屬性" table="維護關(guān)聯(lián)關(guān)系的表名">
            <key column="在維護關(guān)系那里的自己的主鍵"></key>
            <many-to-many  class="關(guān)聯(lián)類" column="關(guān)聯(lián)類的關(guān)聯(lián)id"></many-to-many>
        </set>
    </class>
</hibernate-mapping>
image.png
<?xml version="1.0" encoding="UTF-8"?>
<!-- Student.hbm.xml -->
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cc.sirius.bean">
    <class name="Student" table="t_student"  >
    
        <id name="sid" column="sid">
            <generator class="native"></generator>
        </id>
        <property name="name"></property>
        <property name="sex"></property>

        <set name="courses" table="t_student_course" >
            <key column="sid" not-null="true" ></key>
            <many-to-many  class="Course" column="cid" ></many-to-many>
        </set>

    </class>

</hibernate-mapping>




<?xml version="1.0" encoding="UTF-8"?>
<!-- Course.hbm.xml -->
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cc.sirius.bean">
    <class name="Course" table="t_course">
        
        <id name="cid" column="cid">
            <generator class="native"></generator>
        </id>
        <property name="cname"></property>
    
        <set name="students" table="t_student_course" >
            <key column="cid" not-null="true"></key>
            <many-to-many class="Student" column="sid"></many-to-many>
        </set>
    
    </class>

</hibernate-mapping>

1.1添加


@Test
    public void add() {

        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        Student s1 = new Student();
        s1.setName("旺旺");
        s1.setSex("男");

        Student s2 = new Student();
        s2.setName("小董");
        s2.setSex("男");

        Course c1 = new Course();
        c1.setCname("語文");
        Course c2 = new Course();
        c2.setCname("數(shù)學(xué)");

        // 維護關(guān)系
        s1.getCourses().add(c1);
        s1.getCourses().add(c2);

        s2.getCourses().add(c1);
        s2.getCourses().add(c2);

        session.save(c1);
        session.save(c2);
        session.save(s1);
        session.save(s2);

        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    }


輸出：
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (sid, cid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (sid, cid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (sid, cid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (sid, cid) 
    values
        (?, ?)

1.2 更新

    @Test
    public void update() {
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
            Student student01 = (Student) session.get(Student.class, 1);
            
            Iterator<Course> it = student01.getCourses().iterator();
            int i=0;
            while(it.hasNext()){
                Course c = it.next();
                c.setCname("小白"+i++);
            }
            
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
        
    }

Hibernate: 
    select
        student0_.sid as sid2_0_,
        student0_.name as name2_0_,
        student0_.sex as sex2_0_ 
    from
        t_student student0_ 
    where
        student0_.sid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
[Course [cid=1, cname=語文], Course [cid=2, cname=數(shù)學(xué)]]

1.3 刪除

@Test
    public void deleteOne(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
            session.createQuery("delete from Student where sid=1").executeUpdate();
            
            
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    
    }

Hibernate: 
    delete 
    from
        t_student 
    where
        sid=1
10:46:16,083  WARN JDBCExceptionReporter:233 - SQL Error: 1451, SQLState: 23000
10:46:16,083 ERROR JDBCExceptionReporter:234 - Cannot delete or update a parent row: a foreign key constraint fails (`hbm_rele`.`t_student_course`, CONSTRAINT `FK3F2869CAEE65BEC0` FOREIGN KEY (`sid`) REFERENCES `t_student` (`sid`))
10:46:16,089  INFO SessionFactoryImpl:927 - closing

這里必須先把中間維護關(guān)系的表給更改了才行

@Test
    public void deleteOneWithObj(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        
            Student student = (Student) session.get(Student.class, 1);
            session.delete(student);
            
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    
    }

Hibernate: 
    select
        student0_.sid as sid2_0_,
        student0_.name as name2_0_,
        student0_.sex as sex2_0_ 
    from
        t_student student0_ 
    where
        student0_.sid=?
Hibernate: 
    delete 
    from
        t_student_course 
    where
        sid=?
Hibernate: 
    delete 
    from
        t_student 
    where
        sid=?

2.0 一方放棄維護外鍵（單向多對多）

Student 放棄維護外鍵

<!--student-->
        <set name="courses" table="t_student_course" inverse="true">
            <key column="sid" not-null="true" ></key>
            <many-to-many  class="Course" column="cid" ></many-to-many>
        </set>


  `cid` int(11) NOT NULL,
  `sid` int(11) NOT NULL,
  PRIMARY KEY (`cid`,`sid`),
  KEY `FK3F2869CAEE65BEC0` (`sid`),
  KEY `FK3F2869CA4E48E42` (`cid`),
  CONSTRAINT `FK3F2869CA4E48E42` FOREIGN KEY (`cid`) REFERENCES `t_course` (`cid
`),
  CONSTRAINT `FK3F2869CAEE65BEC0` FOREIGN KEY (`sid`) REFERENCES `t_student` (`s
id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

2.1 調(diào)用上面的add函數(shù)

Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)

這里并不在中間表做關(guān)系維護,直白一點都办，就是說Student已經(jīng)不關(guān)心Course了势木，所以如果通過把Course 添加到Student的set里歌懒，并不能維護關(guān)系及皂。

反過來验烧，這里用course 添加student就可以維護關(guān)系噪窘，hibernate依然會在數(shù)據(jù)庫中通過中間表來維護關(guān)系倔监。


    @Test
    public void addInverseFalse() {

        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        Student s1 = new Student();
        s1.setName("旺旺");
        s1.setSex("男");

        Student s2 = new Student();
        s2.setName("小董");
        s2.setSex("男");

        Course c1 = new Course();
        c1.setCname("語文");
        Course c2 = new Course();
        c2.setCname("數(shù)學(xué)");

        // 維護關(guān)系
        c1.getStudents().add(s1);
        c1.getStudents().add(s2);
        
        c2.getStudents().add(s1);
        c2.getStudents().add(s2);

        session.save(c1);
        session.save(c2);
        session.save(s1);
        session.save(s2);

        // ------------------------------------------------------
        session.getTransaction().commit();
        // session.close();
    }


Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)

所以静暂，同理有：通過Student刪除洽蛀，中間表的關(guān)系不會刪除郊供，通過Student得到Course并且施加更新驮审，不會生效疯淫。

既然你放棄了她熙掺，你給的東西咕宿，再好她也不要。
勉強得到的载城，不過是幻夢诉瓦。（通過Student得到Course睬澡，修改并不會寫入）

2.2 更新和刪除

調(diào)用上面的update()

Hibernate: 
    select
        student0_.sid as sid2_0_,
        student0_.name as name2_0_,
        student0_.sex as sex2_0_ 
    from
        t_student student0_ 
    where
        student0_.sid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?

如果中間表有關(guān)系煞聪，也就是數(shù)據(jù)是通過Course維護的昔脯，deleteOne()

Hibernate: 
    delete 
    from
        t_student 
    where
        sid=2
11:16:53,179  WARN JDBCExceptionReporter:233 - SQL Error: 1451, SQLState: 23000
11:16:53,180 ERROR JDBCExceptionReporter:234 - Cannot delete or update a parent row: a foreign key constraint fails (`hbm_rele`.`t_student_course`, CONSTRAINT `FK3F2869CAEE65BEC0` FOREIGN KEY (`sid`) REFERENCES `t_student` (`sid`))
11:16:53,188  INFO SessionFactoryImpl:927 - closing

3.0級聯(lián)加載

3.1Student放棄維護Course云稚，并且級聯(lián)加載Course

不愛了静陈，為什么還藕斷絲連地關(guān)心鲸拥。

<!--student-->
        <set name="courses" table="t_student_course" inverse="true" cascade="all">
            <key column="sid" not-null="true" ></key>
            <many-to-many  class="Course" column="cid" ></many-to-many>
        </set>



    @Test
    public void addInverseTrueCascadeAll() {

        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        Student s1 = new Student();
        s1.setName("旺旺");
        s1.setSex("男");

        Student s2 = new Student();
        s2.setName("小董");
        s2.setSex("男");

        Course c1 = new Course();
        c1.setCname("語文");
        Course c2 = new Course();
        c2.setCname("數(shù)學(xué)");

        // 維護關(guān)系
        c1.getStudents().add(s1);
        c1.getStudents().add(s2);
        
        c2.getStudents().add(s1);
        c2.getStudents().add(s2);

        session.save(c1);
        session.save(c2);

        // ------------------------------------------------------
        session.getTransaction().commit();
        // session.close();
    }


Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
//error

這里會出錯懂衩，因為student放棄了維護勃痴，雖然student級聯(lián)了course,而course并沒有級聯(lián)student;

可以想象沛申，這里的查詢應(yīng)該可以成功

    
    @Test
    /*
     * student
     *      Inverse:    true
     *      Cascade:    all
     */
    public void findCascadeAll() {
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
            Student student01 = (Student) session.get(Student.class, 1);
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
        
        System.out.println(student01.getCourses());//沒辦法找到铁材，這里
    }

結(jié)果卻是：

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: cc.sirius.bean.Student.courses, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:368)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)
    at org.hibernate.collection.PersistentSet.toString(PersistentSet.java:332)
    at java.lang.String.valueOf(String.java:2994)
    at java.io.PrintStream.println(PrintStream.java:821)
    at cc.sirius.service.TestDo2.findCascadeAll(TestDo2.java:138)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at ...

這里是懶加載的問題村生，
set 的lazy默認(rèn)為true趁桃。修改為false


        <set name="courses" table="t_student_course" inverse="true" lazy="false" cascade="all">
            <key column="sid" not-null="true" ></key>
            <many-to-many  class="Course" column="cid" ></many-to-many>
        </set>

Hibernate: 
    select
        student0_.sid as sid2_0_,
        student0_.name as name2_0_,
        student0_.sex as sex2_0_ 
    from
        t_student student0_ 
    where
        student0_.sid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
[]

3.2刪除

至于刪除，如果是student典徘，他放棄了維護外鍵,但是配置了級聯(lián)刪除

@Test
    public void deleteOneWithObj(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        
            Student student = (Student) session.get(Student.class, 1);
            session.delete(student);
            
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    
    }

Hibernate: 
    select
        student0_.sid as sid2_0_,
        student0_.name as name2_0_,
        student0_.sex as sex2_0_ 
    from
        t_student student0_ 
    where
        student0_.sid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
Hibernate: 
    delete 
    from
        t_student_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_student_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_student 
    where
        sid=?
  • 刪除student02的時候帜平，先查找student02
  • 查找student02的 course
  • 在關(guān)聯(lián)表中把和student選過的課全刪了（這里不是只刪除student-course那些行）
  • 然后在course中刪除student學(xué)過的所有課程
  • 最后才是刪除student

4.0 Student放棄維護Course，并且雙方都級聯(lián)加載對方

他主動放棄淑掌，雙方卻還牽掛著彼此

為了效果明顯抛腕，這里懶加載都關(guān)掉

4.1 級聯(lián)插入

public void addInverseTrueCascadeAll() {

        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        Student s1 = new Student();
        s1.setName("旺旺");
        s1.setSex("男");

        Student s2 = new Student();
        s2.setName("小董");
        s2.setSex("男");

        Course c1 = new Course();
        c1.setCname("語文");
        Course c2 = new Course();
        c2.setCname("數(shù)學(xué)");

        // 維護關(guān)系
        c1.getStudents().add(s1);
        c1.getStudents().add(s2);
        
        c2.getStudents().add(s1);
        c2.getStudents().add(s2);

        session.save(c1);
        session.save(c2);

        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    }

效果：

Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student
        (name, sex) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_course
        (cname) 
    values
        (?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        t_student_course
        (cid, sid) 
    values
        (?, ?)

4.2 級聯(lián)更新


public void updateCascadeAll() {
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------

        Course course=(Course) session.get(Course.class,1);
        Iterator<Student> it = course.getStudents().iterator();
        
        while(it.hasNext()){
            it.next().setName("灰太狼");
        }
            
        session.save(course);
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
        
    }


Hibernate: 
    select
        course0_.cid as cid0_0_,
        course0_.cname as cname0_0_ 
    from
        t_course course0_ 
    where
        course0_.cid=?
Hibernate: 
    select
        students0_.cid as cid0_1_,
        students0_.sid as sid1_,
        student1_.sid as sid2_0_,
        student1_.name as name2_0_,
        student1_.sex as sex2_0_ 
    from
        t_student_course students0_ 
    inner join
        t_student student1_ 
            on students0_.sid=student1_.sid 
    where
        students0_.cid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
Hibernate: 
    select
        students0_.cid as cid0_1_,
        students0_.sid as sid1_,
        student1_.sid as sid2_0_,
        student1_.name as name2_0_,
        student1_.sex as sex2_0_ 
    from
        t_student_course students0_ 
    inner join
        t_student student1_ 
            on students0_.sid=student1_.sid 
    where
        students0_.cid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
Hibernate: 
    update
        t_student 
    set
        name=?,
        sex=? 
    where
        sid=?
Hibernate: 
    update
        t_student 
    set
        name=?,
        sex=? 
    where
        sid=?
image.png

4.3 地獄級別的刪除


    @Test
    public void deleteCourse(){
        Session session = HibernateUtils.openSession();
        session.beginTransaction();
        // -----------------------------------------------------
        
            Course course = (Course) session.get(Course.class, 1);
            session.delete(course);
        // ------------------------------------------------------
        session.getTransaction().commit();
        session.close();
    
    }


Hibernate: 
    select
        course0_.cid as cid0_0_,
        course0_.cname as cname0_0_ 
    from
        t_course course0_ 
    where
        course0_.cid=?
Hibernate: 
    select
        students0_.cid as cid0_1_,
        students0_.sid as sid1_,
        student1_.sid as sid2_0_,
        student1_.name as name2_0_,
        student1_.sex as sex2_0_ 
    from
        t_student_course students0_ 
    inner join
        t_student student1_ 
            on students0_.sid=student1_.sid 
    where
        students0_.cid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
Hibernate: 
    select
        students0_.cid as cid0_1_,
        students0_.sid as sid1_,
        student1_.sid as sid2_0_,
        student1_.name as name2_0_,
        student1_.sex as sex2_0_ 
    from
        t_student_course students0_ 
    inner join
        t_student student1_ 
            on students0_.sid=student1_.sid 
    where
        students0_.cid=?
Hibernate: 
    select
        courses0_.sid as sid2_1_,
        courses0_.cid as cid1_,
        course1_.cid as cid0_0_,
        course1_.cname as cname0_0_ 
    from
        t_student_course courses0_ 
    inner join
        t_course course1_ 
            on courses0_.cid=course1_.cid 
    where
        courses0_.sid=?
Hibernate: 
    delete 
    from
        t_student_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_student_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_student 
    where
        sid=?
Hibernate: 
    delete 
    from
        t_course 
    where
        cid=?
Hibernate: 
    delete 
    from
        t_student 
    where
        sid=?
Hibernate: 
    delete 
    from
        t_course 
    where
        cid=?
  • 查找course01
  • 查找course01底下所有student
  • 查找student對應(yīng)所有course
  • 一直查找，直到course和student之間不再有關(guān)聯(lián)
  • 然后先刪除中間表
  • 再刪除兩個表的數(shù)據(jù)
  • 結(jié)局是兩個表的數(shù)據(jù)基本全廢了刹悴，等于清表
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