How to do this using django object query:
SELECT * FROM test WHERE (test_id IN (SELECT test_id FROM test_subject_set)) AND (test_begin_time < '') AND (test_end_time > '')
The model:
class Test(models.Model):
id = models.AutoField(primary_key=True)
user = models.ForeignKey(User)
groups = models.ManyToManyField(Group)
class TestSubjectSet(models.Model):
id = models.AutoField(primary_key=True)
test = models.ForeignKey(Test)
Two querysets are documented way of doing this. It will be one database hit anyway.
test_ids = Subject.objects.all()
result = Test.objects.filter(test_id__in=test_ids).filter([some other filtering])
DrTyrsa just about had it.
test_ids = list(TestSubjectSet.objects.all().values_list('test_id', flat=True))
result = Test.objects.filter(id__in=test_ids, test_begin_time__lt='', test_end_time__gt='')
The way Tyrsa was doing it would not give you a list of the Test ids from TestSubjectSet, but instead give you a TestSubjectSet queryset.
Also, I was confused by the test_begin_time and test_end_time fields, because you didn't mention them in your models.
Update: Used list() on the queryset, because, according to the link DrTyrsa posted, DBs "don't optimize nested querysets very well".