Prevent duplicate Resources from being created

[pricem]

Stanford ESP had a problem with Ajax scheduling that turned out to be caused by multiple Resource objects existing for a given (room name, timeslot ID) combination. This should be prevented, and also probably enforced by a unique_together constraint.

[btidor]

Per #2036, name and event (?) should also be unique_together

[lenaqr]

Yeah, event and timeslot ID are the same thing.

[willgearty]

For future reference: https://docs.djangoproject.com/en/1.11/ref/models/options/#unique-together

[willgearty]

Making these fields "unique_together" would break the current implementation of floating resources, which allows for duplicates (#2840):

ESP-Website/esp/esp/resources/models.py

Lines 220 to 222 in 76a45d2

	def duplicates(self):
	res_list = Resource.objects.filter(name=self.name, event = self.event)
	return res_list

[willgearty]

It is not currently possible to create two classrooms with the same name with the normal classroom UI. When trying to add a new classroom with the same name, the code below uses the existing classroom and updates it instead:

ESP-Website/esp/esp/program/modules/forms/resources.py

Lines 202 to 215 in c292a39

	if orig_room_number == "":
	orig_room_number = self.cleaned_data['room_number']
	initial_rooms = program.getClassrooms().filter(name=orig_room_number).distinct()
	initial_furnishings = {}
	for r in initial_rooms:
	initial_furnishings[r] = list(r.associated_resources())
	timeslots = Event.objects.filter(id__in=[int(id_str) for id_str in self.cleaned_data['times_available']])
	rooms_to_keep = list(initial_rooms.filter(event__in=timeslots))
	rooms_to_delete = list(initial_rooms.exclude(event__in=timeslots))
	new_timeslots = timeslots.exclude(id__in=[x.event_id for x in rooms_to_keep])