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

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?

CodePudding user response：

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/

CodePudding user response：

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.