Is it best practice to define a join table for Django many to many relationships?

Question

I have the following code:

class Tutors(models.Model):
    first_name = models.CharField(max_length=20, default=None, blank=False) #you need to add default none and blank false to enforce the Not-Null constraint
    last_name = models.CharField(max_length=20, default=None, blank=False)
    email = models.EmailField(max_length=254,default=None, blank=False)
    birth_day = models.DateField(auto_now=False, auto_now_add=False, default=False, blank=False)

    def __str__(self):
        return(self.first_name + ' ' + self.last_name)

        
class ArtSubjects(models.Model):
    subject_name = models.CharField(max_length=20, default=None, blank=False)
    tutors = models.ManyToManyField(Tutors)

    def __str__(self):
        return self.subject_name

My question is, should I define many to many relationships like this? Or should I define a new class for the table?

The reason I ask is that I can get objects from the join table by querying by ArtSubjects class like so - adobeAI.tutors.all() returns <QuerySet [<Tutors: Matt Aird>, <Tutors: Tom John>]>

But I can't think of a way for querying the join table by tutors to see what classes an individual tutor teaches.

Any advice on this?

Answer 1

You can query tutors the same way. Here's an axample:

john = Tutors.objects.get(first_name="John")
john.artsubjects_set.all()

If you like to have a more readable name than _set , add a related_name on the ManyToManyField field:

class ArtSubjects(models.Model):
    tutors = models.ManyToManyField(Tutors, related_name="teaches")
    ...

john.teaches.all()

You can find more details in the documentation https://docs.djangoproject.com/en/3.2/topics/db/examples/many_to_many/

Answer 2

This can be done (see https://docs.djangoproject.com/en/3.2/topics/db/models/#extra-fields-on-many-to-many-relationships ), but if you're not adding additional data to the intermediary model I wouldn't recommend it.

Django will create the intermediary model behind the scenes. In this case it would be accessible as ArtSubjects.tutors.through .

See @Marco's answer for how to query the relationship.