我有这两类(表)
@Entity
@Table(name = "course")
public class Course {
@Id
@Column(name = "courseid")
private String courseId;
@Column(name = "coursename")
private String courseName;
@Column(name = "vahed")
private int vahed;
@Column(name = "coursedep")
private int dep;
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "student_course", joinColumns = @JoinColumn(name = "course_id"), inverseJoinColumns = @JoinColumn(name = "student_id"))
private Set<Student> student = new HashSet<Student>();
//Some setter and getter
和这个:
@Entity
@Table(name = "student")
public class Student {
@Id
@Column(name="studid")
private String stId;
@Column(nullable = false, name="studname")
private String studName;
@Column(name="stmajor")
private String stMajor;
@Column(name="stlevel", length=3)
private String stLevel;
@Column(name="stdep")
private int stdep;
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "student_course"
,joinColumns = @JoinColumn(name = "student_id")
,inverseJoinColumns = @JoinColumn(name = "course_id")
)
private Set<Course> course = new HashSet<Course>();
//Some setter and getter
运行此代码后,在数据库(student_course)中创建了一个额外的表,现在我想知道如何在此表中添加额外的字段,例如(Grade、Date 和...(我的意思是student_course 表))
我看到了一些解决方案,但我不喜欢它们,而且我也有一些问题:
第一个样品 http://boris.kirzner.info/blog/archives/2008/07/19/hibernate-annotations-the-many-to-many-association-with-composite-key/
如果您在链接表(STUDENT_COURSE)上添加额外的字段,您必须根据 skaffman 的答案或另一个如下所示的答案选择一种方法。
有一种方法,其中链接表(STUDENT_COURSE)的行为类似于 @Embeddable,根据:
@Embeddable
public class JoinedStudentCourse {
// Lets suppose you have added this field
@Column(updatable=false)
private Date joinedDate;
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="STUDENT_ID", insertable=false, updatable=false)
private Student student;
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="COURSE_ID", insertable=false, updatable=false)
private Course course;
// getter's and setter's
public boolean equals(Object instance) {
if(instance == null)
return false;
if(!(instance instanceof JoinedStudentCourse))
return false;
JoinedStudentCourse other = (JoinedStudentCourse) instance;
if(!(student.getId().equals(other.getStudent().getId()))
return false;
if(!(course.getId().equals(other.getCourse().getId()))
return false;
// ATT: use immutable fields like joinedDate in equals() implementation
if(!(joinedDate.equals(other.getJoinedDate()))
return false;
return true;
}
public int hashcode() {
// hashcode implementation
}
}
因此,您将同时参加学生课程和课程课程
public class Student {
@CollectionOfElements
@JoinTable(
table=@Table(name="STUDENT_COURSE"),
joinColumns=@JoinColumn(name="STUDENT_ID")
)
private Set<JoinedStudentCourse> joined = new HashSet<JoinedStudentCourse>();
}
public class Course {
@CollectionOfElements
@JoinTable(
table=@Table(name="STUDENT_COURSE"),
joinColumns=@JoinColumn(name="COURSE_ID")
)
private Set<JoinedStudentCourse> joined = new HashSet<JoinedStudentCourse>();
}
请记住:@Embeddable 类的生命周期绑定到所属实体类(Student 和 Course),因此请注意它。
建议:Hibernate 团队支持这两种方法(@OneToMany(schiffman 的答案)或 @CollectionsOfElements),因为 @ManyToMany 映射 - 级联操作存在一些限制。
regards,
本文内容由网友自发贡献,版权归原作者所有,本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容,请联系:hwhale#tublm.com(使用前将#替换为@)