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我有一个按以下方式建模的现有数据库：

学生- SchoolId(PK), StudentId(PK),StudentName

老师- SchoolId(PK), TeacherId(PK),TeacherName

Student_Teacher - SchoolId(PK), StudentId(PK),TeacherId(PK)

外键引用存在于Student_Teacher各个实体。

现在我正在为这个现有数据库创建休眠实体。我在创建从学生到老师的多对多映射时遇到了奇怪的问题。

@Entity
@Table(name = "Student")
public class Student {
    @EmbeddableId
    private StudentPK itemId;

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

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name="Student_Teacher", joinColumns={@JoinColumn(name="SchoolId", referencedColumnName="SchoolId"),@JoinColumn(name="StudentId", referencedColumnName="StudentId")}, inverseJoinColumns={@JoinColumn(name="SchoolId", referencedColumnName="SchoolId"),@JoinColumn(name="TeacherId", referencedColumnName="TeacherId")})
    private List<Teacher> attachments=new ArrayList<Teacher>();
}

上面的代码包含一些重复的SchoolId引用。

有任何想法吗？

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2 回答 2

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我看到您的实体映射存在问题，应该如下

学校- school_id(PK),school_name

学生- student_id(PK),student_name,fk_school_id(FK),

老师-teacher_id(PK),teacher_name,fk_school_id(FK)

*学生老师* - student_teacher_id(PK), fk_student_id(FK),fk_teacher_id(FK)

和实体类如下

学校实体

@Entity
@Table(name = "school")
public class School {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column (name = "school_id")
   private int Id;

    @Column(name="school_name")
    private String schoolName;  

   @OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
   private Set<Student> students = new HashSet<Student>  

   @OneToMany(fetch = FetchType.LAZY, mappedBy = "school")
   private Set<Teacher> teachers = new HashSet<Teacher> 
}

学生实体

@Entity
@Table(name = "student")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column (name = "student_id")
    private int Id;

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

   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "school_id", nullable = false)
   private School school;       

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "student_teacher", joinColumns = {@JoinColumn(name = "fk_student_id") }, inverseJoinColumns = { @JoinColumn(name = "fk_teacher_id") })
    private List<Teacher> teachers = new ArrayList<Teacher>();

}

教师实体

@Entity
@Table(name = "teacher")
public class Teacher {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column (name = "teacher_id")
    private int Id;

    @Column(name="teacher_name")
    private String name;

   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "school_id", nullable = false)
   private School school;   

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "student_teacher", joinColumns = {@JoinColumn(name = "fk_teacher_id") }, inverseJoinColumns = { @JoinColumn(name = "fk_student_id") })
    private List<Student> students =new ArrayList<Student>();
}

希望这能解决这个问题..

由于您已在 Student_Teacher 表中将“SchoolId”声明为PK，因此不允许您为 Student_Teacher 表的 SchoolId 字段添加重复条目，但事实并非如此。因此上述关系将给出重复的 SchoolId 参考。当您要将来自同一所学校的两个不同学生添加到Student_Teacher表中时..

于 2013-09-04T11:31:04.760 回答
0

您是否将每个实体的各种 PK 定义为复合键，因为我注意到每个实体使用多个 PK。是否有任何限制，为什么您不能为每个实体使用一个单独的 PK，而只使用关系表来绑定 2 个实体？

于 2013-09-04T10:56:00.230 回答