simple django join query without foreign key - mysql

Question

** Below are two models teacher and loginstudent, A teacher can teach multiple sections and multiple students can be in same section.So section field cannot be a foreign key.If I want to find out all courses taken by a particular student,what should I do? Is there any simple django query just like sql did.How to do?
**
class Teacher(models.Model):
username=models.CharField(max_length=50)
password=models.CharField(max_length=89)
course=models.CharField(max_length=30)
section=models.CharField(max_length=30)
class LoginStudent(models.Model):
username=models.CharField(max_length=50)
password=models.CharField(max_length=89)
section=models.CharField(max_length=30)

Answer 1

OK, I would recommend to stick to the default user system from Django and build one-to-one profiles of the specific type where needed. Latter on you can differentiate between the users based on the value of the foreign key or you could implement permissions which are tied to the user type
from django.db.models.query_utils import Q
# for example, this could be a way to extend users to hold teachers and students
class TeacherProfile(models.Model):
user = models.OneToOneField(User, related_name='teacher_profile')
# other relevant teacher profile items
ONLY_TEACHERS_FILTER = Q(teacher_profile__isnull=False) & Q(student_profile__isnull=True)
class StudentProfile(models.Model):
user = models.OneToOneField(User, related_name='student_profile')
# other relevant student profile items
sections = models.ManyToManyField('Section', related_name='students') # mind the quotes to Section name
class Section(models.Model)
name = models.CharField(max_length=50)
# other section fields goes here...
class Course(models.Model):
name = models.CharField(max_length=50)
teacher = models.ForeingKey(User, related_name='courses', limit_choices_to=ONLY_TEACHERS_FILTER)
sections = models.ManyToManyField(Section, related_name='courses')
Now to answer to the question what are the courses to which a student attends to:
queryset = Course.objects.filter(section__students__in=[user])
Hope it helps!