一對多休眠保存級聯問題

Question

我與Hibernate和OneToMany Relationship合作時，今天遇到了奇怪的行為， 盡管我是故意這樣做的，但我並不期望這種行為

College.java

@Entity
@Table(name="COLLEGE")
public class College implements Serializable{
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="COLLEGE_XID")
    private Long collegeId;

    @Column(name="COLLEGE_NAME")
    private String collegeName;

    @OneToMany(mappedBy="college",cascade = CascadeType.ALL) 
    private List<Student> studentList = new ArrayList<Student>();
    //... with get and setters
}

學生.java

@Entity
@Table(name = "STUDENT")
public class Student implements Serializable    {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="STUDENT_XID")
    private Long studentId;

    @Column(name="STUDENT_NAME")
    private String studentName;

    @ManyToOne
    @JoinColumn(name="COLLEGE_XID",nullable=false)
    private College college;
    //... with get and setters
}

應用程序

    College college1 = new BdCollege();
    college1.setCollegeName("C_1");

    College college2 = new BdCollege();
    college2.setCollegeName("C_2");

    Student student1 = new BdStudent();
    student1.setStudentName("S_1_C_2");

    CollegeDAO collegeDAO = new  CollegeDAO();

    // setting student 1 Parent to College 1        
    student1.setCollege(college1);   // <---- Here the Issue  ... student 1 as college 1 child

    // BUT assigning Student 1 as Child of Collge 2 in List 
    // i did it purposely to test the behaviour
    college2.getStudentList().add(student1);  // <---- Here the Issue ... but assigning it in the list of College 2 ... ws expecting Exception 

     // Saved College 1 & 2
     collegeDAO.save(college1);
     collegeDAO.save(college2);

      // Saved Successfully BUT

結果學院表

 COLLEGE_XID     COLLEGE_NAME    
 --------------  --------------- 
 1               C_1             
 2               C_2 

學生表

 STUDENT_XID     STUDENT_NAME     COLLEGE_XID    
 --------------  ---------------  -------------- 
 1               S_1_C_2          1   

我期待一些例外，因為孩子和父母在大學里的作業不匹配-學生的例子和讓我感到困擾的另一件事是休眠模式生成的查詢

Hibernate: insert into COLLEGE (COLLEGE_NAME) values (?)
Hibernate: insert into COLLEGE (COLLEGE_NAME) values (?)
Hibernate: insert into STUDENT (COLLEGE_XID, STUDENT_NAME) values (?, ?)

也就是說，它首先保存College 1，然后保存College 2，然后將學生保存為College 2的孩子，但結果顯示為College 1的孩子

Answer 1

這是因為您添加了mappingBy屬性並使學生成為協會的所有者。 由於學生實體是所有者，因此它將維持關系，並且休眠狀態將忽略學院方面的更改。