public ActionResult DeleteLecturer(int lecturerId)
{
/*
* Deleting a lecturer is quite an impactful action to the system's data because a lecturer record
* has its primary key (student_id) as a foriegn key in other entities, thus prompting the associated
* records in those entities to also be deleted.
*
* The worst case scenario for this, is when the deletion of a lecturer affects n number of entities (prompting their records to be removed also), where n is the maximum number of entities that
* can be affected.
*
* This scenario occurs when the FYP time-period has commenced and the lecturer, being in supervision
* of FYP group(s) and also, happened to propose "lecturer-intiated" projects and made announcements
* (also attaching file resources to at least one of the announcement(s)) before (the commenement of
* the FYP time-period), has decided to leave SP. In this worst case scenario, n turns out to be 4
* (The four affected entities are namely; Announcement, File_Resource, Group,
* Industry_Lecturer_Project).
*
* Superificially, it might seem OK to have those record(s) in (all) the associated tables, deleted.
* However practically, it would make no sense, to have a group (with students in it deleted) merely
* because its supervisor has left SP.
*
* Hence, in practicality n would be modified as; n = 4 - 1 = 3, where the entity, "exempted" from
* deletion is; Group.
*
* Additionally, it should be noted that n can be further reduced to; n = 3 - 2 = 1, where the
* additional two entities, which should also be exempted deletion (alike the above-mentioned
* Group entity) are; Announcement and File_Resource. However due to technical database
* constraint, those two entities would not be removed from deletion. Thus, n is still; 3.
*
* Also, like Group, the records in the Industry_Lecturer_Project entity should not be deleted. Thus
* n = 3 - 1 = 2;
*
* Hence as dicussed above, in the worst case scenario, only at most n entities can be affected, where
* n is revealed to be 2. The affected entities are thus Announcement and File_Resource.
*
* Thus, with the above discussion, the code below deletes associated records from the the Announcement
* and File_Resource entity.
*/
// Variable declaration and initialization.
int numberOfRowsAffected = 0;
IAnnouncementRepository announcementRepository = new AnnouncementRepository();
IFileResourceRepository fileResourceRepository = new FileResourceRepository();
IProjectRepository projectRepository = new ProjectRepository();
IGroupRepository groupRepository = new GroupRepository();
IEnumerable <Announcement> associatedAnnouncements = null;
IEnumerable <object> associatedGroups = null;
IEnumerable <dynamic> associatedIndustryLecturerProjects = null;
try
{
associatedAnnouncements = announcementRepository.GetAnnouncementsByLecturerId(lecturerId);
// Deleting records from the File_Resource entity.
foreach (Announcement announcement in associatedAnnouncements)
{
fileResourceRepository.DeleteFileResourcesForAnnouncement(announcement.announcement_id);
}
// Deleting Announcement's records.
announcementRepository.DeleteAnnouncementsForLecturer(lecturerId);
associatedGroups = groupRepository.GetGroupsByLecturerId(lecturerId);
// Disassociating any group records which are currently associated to the (to be) deleted lecturer record, by setting the group_role field in the Group entity to NULL.
foreach (object group in associatedGroups)
{
int groupId = int.Parse(group.GetType().GetProperty("groupId").GetValue(group, null).ToString());
groupRepository.AssignSupervisor(null, groupId);
}
associatedIndustryLecturerProjects = projectRepository.GetIndustryLecturerProjectsByLecturerId(lecturerId);
// Disassociating any project records which are currently associated to the (to be) deleted lecturer record, by setting the lecturer_id field in the Lecturer entity to NULL.
foreach (dynamic project in associatedIndustryLecturerProjects)
{
projectRepository.SetLecturerId(project.project_id, null);
}
// Finally, once all records are properly settled, as from above, delete the lecturer (from the Lecturer entity).
numberOfRowsAffected = lecturerRepository.DeleteLecturer(lecturerId);
return(Json(new { rowsAffected = numberOfRowsAffected }));
}
catch (Exception e)
{
return(Json(new { rowsAffected = numberOfRowsAffected, error = e.Message }));
}
}