How to check if the object is assigned to another object | Django - django

Question

I am working on a django case like below:
models.py
class Room(models.Model):
name = models.CharField("Room No.",max_length=200)
class Meta:
verbose_name_plural = "Room"
def __str__(self):
return self.name
class Student(models.Model):
name = models.CharField("name",max_length=200)
father_name = models.CharField("father Name",max_length=200)
cell_no = models.CharField("cell No",max_length=200)
address = models.CharField("address",max_length=500)
room = models.ForeignKey(Room, on_delete=models.CASCADE, null=True, blank=True, related_name='all_rooms')
class Meta:
verbose_name_plural = "Student"
def __str__(self):
return self.name
views.py
def room(request):
allrooms= Room.objects.all()
form = RoomForm(request.POST or None, request.FILES or None)
if form.is_valid():
form.save()
messages.success(request, "Room added successfully.")
return redirect('/room')
context = {'allrooms':allrooms, 'form':form}
return render(request, 'room.html', context)
In templates in room.html I want to show the status Vacant/Occupied based on the fact if a room is assigned to some student or not. I have the following code in template but it shows 'Vacant' status for all rooms.
<table id="example1" class="table table-bordered table-striped">
<thead>
<tr>
<th>Room</th>
<th class="text-center">Status</th>
<th class="text-center">Action</th>
</tr>
</thead>
<tbody>
{% for room in allrooms %}
<tr>
<td>{{ room.name }}</td>
<td class="text-center">
{% if room.student_set.all %}
<small class="badge badge-danger">Occupied</small>
{% elif not room.student.all %}
<small class="badge badge-success">Vacant</small>
{% endif %}
</td>
<td class="text-center"><i class="fas fa-edit"></i></td>
</tr>
{% endfor %}
</tbody>
</table>
Please help someone to show he status of the room.

Answer 1

to get assigned and unassigned rooms you have to write queries with respect to the related field(in this case the foreign key "all_rooms") as follows:
total_rooms = Room.objects.all().annotate(num_rooms=Count("all_rooms"))
assigned_rooms = total_rooms.filter(num_rooms__gt=0)
unassigned_rooms = total_rooms.exclude(num_rooms__gt=0)
On running, these queries will return the room instances: