EJB notes three steps to success

Multiple-to-multiple relationships use the ing policy of the intermediate table connection. The created intermediate table introduces the primary keys on both sides as foreign keys.

@ 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 defines student as the maintenance end of the bidirectional relationship.
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")}, // Foreign key of the maintained end
Inversejoincolumns =... {@ joincolumn (name = "student_id", referencedcolumnname = "studentid")}) // maintenance end foreign key
Public set <student> getstudents ()...{
Return students;
}
Public void setstudents (set <student> students )...{
This. Students = students;
}

Public void addstudent (Student )...{
If (! This. Students. Contains (student ))...{
This. Students. Add (student );
}
}

Public void removestudent (Student )...{
This. Students. Remove (student );
}
}