I am trying to reduce my complexity by doing the following. I am trying to get all the teachers in active classrooms.
teacher/models.py:
Teacher(models.Model):
name = models.CharField(max_length=300)
classroom/models.py:
Classroom(models.Model):
name = models.CharField(max_length=300)
teacher = models.ForeignKey(Teacher)
students = models.ManyToManyField(Student)
status = models.CharField(max_length=50)
admin/views.py
teachers = Teacher.objects.prefetch_related(Prefetch('classroom_set',queryset=Classroom.objects.filter(status='Active'))
for teacher in teachers:
classrooms = teacher.all()
# run functions
By doing this I get teachers with classrooms. But it also returns teachers with no active classrooms(empty list) which I don't want. Because of this, I have to loop around thousands of teachers with empty classroom_set. Is there any way I can remove those teachers whose classroom_set is [ ]?
This is my original question - Django multiple queries with foreign keys
Thanks
If you want all teachers with at least one related active class, you do not need to prefetch these, you can filter on the related objects, like:
Teacher.objects.filter(class__status='Active').distinct()If you want to filter the classroom_set as well, you need to combine filtering as well as .prefetch_related:
from django.db.models import Prefetch
Teacher.objects.filter(
class__status='Active'
).prefetch_related(
Prefetch('class_set', queryset=Class.objects.filter(status='Active'))
).distinct()Here we thus will filter like:
SELECT DISTINCT teacher.*
FROM teacher
JOIN class on class.teacher_id = teacher.id
WHERE class.status = 'Active'