EJB笔记三 many to many

多对多关系采用 中间表连接的映射策略。建立的中间表将分别引入两边的主键做为外键

@SuppressWarnings( " serial " )
@Entity
@Table(name  =   " Student " )
public   class  Student implements Serializable ... {
    private Integer studentid;
    private String StudentName;    
    private Set<Teacher> teachers = new HashSet<Teacher>();
  
    public Student() ...{}
    
    public Student(String studentName) ...{
        StudentName = studentName;
    }
    
    @Id
    @GeneratedValue
    public Integer getStudentid() ...{
        return studentid;
    }
    public void setStudentid(Integer studentid) ...{
        this.studentid = studentid;
    }
    
    @Column(nullable=false, length=32)
    public String getStudentName() ...{
        return StudentName;
    }
    public void setStudentName(String studentName) ...{
        StudentName = studentName;
    }
    
    @ManyToMany(mappedBy = "students") //mappedBy定义了student为双向关系的维护端
    public Set<Teacher> getTeachers() ...{
        return teachers;
    }
    public void setTeachers(Set<Teacher> teachers) ...{
        this.teachers = teachers;
    }
}

 

 

@SuppressWarnings( " serial " )
@Entity
@Table(name  =   " Teacher " )
public   class  Teacher implements Serializable ... {
    private Integer teacherid;
    private String TeacherName;    
    private Set<Student> students = new HashSet<Student>();
  
    public Teacher() ...{}
    
    public Teacher(String teacherName) ...{
        TeacherName = teacherName;
    }
    
    @Id
    @GeneratedValue
    public Integer getTeacherid() ...{
        return teacherid;
    }
    public void setTeacherid(Integer teacherid) ...{
        this.teacherid = teacherid;
    } 
    
    @Column(nullable=false, length=32)
    public String getTeacherName() ...{
        return TeacherName;
    }
    public void setTeacherName(String teacherName) ...{
        TeacherName = teacherName;
    }
    
    @ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY) 
    @JoinTable(name = "Teacher_Student",
        joinColumns = ...{@JoinColumn(name = "Teacher_ID", referencedColumnName = "teacherid")},//被维护端的外键
        inverseJoinColumns = ...{@JoinColumn(name = "Student_ID", referencedColumnName = "studentid")})//维护端的外键
    public Set<Student> getStudents() ...{
        return students;
    }
    public void setStudents(Set<Student> students) ...{
        this.students = students;
    }
    
    public void addStudent(Student student) ...{
        if (!this.students.contains(student)) ...{
             this.students.add(student);
        }
    }

     public void removeStudent(Student student) ...{
         this.students.remove(student);
    } 
}