Django中两个模型之间的ManyToMany关系

Question

I am trying to build a website that users can add the courses they are taking. I want to know how should I add the ManyToMany relationship. Such that we can get all users in a course based on the course code or instructor or any field. And we can also get the courses user is enrolled in. Currently, my Database structure is:

class Course(models.Model):
    course_code = models.CharField(max_length=20)
    course_university = models.CharField(max_length=100)
    course_instructor = models.CharField(max_length=100)
    course_year = models.IntegerField(('year'), validators=[MinValueValidator(1984), max_value_current_year])

    def __str__(self):
        return self.course_code

and my user model:

class Profile(AbstractUser):
    bio = models.TextField()
    image = models.ImageField(default='defaults/user/default_u_i.png', 
    courses = models.ManyToManyField('home.Course',related_name='courses')

    def __str__(self):
        return self.username

I was wondering should ManyToMany relationship be in User model or the course model? Or will it make any difference at all?

EDIT : For adding course to post object now I am using this view but it seems to not work:

@login_required
def course_add(request):

    if request.method == "POST":
        form = CourseForm(request.POST or none)
        if form.is_valid():
            course = form.save()
            request.user.add(course)
    else:
        form = CourseForm
    context = {
        'form':form
    }
    return render(request,'home/courses/course_add.html', context)

Answer 1

For a relational databases, the model where you define the ManyToManyField does not matter. Django will create an extra table with two ForeignKey s to the two models that are linked by the ManyToManyField .

The related managers that are added, etc. is all Django logic. Behind the curtains, it will query the table in the middle.

You however need to fix the related_name=… parameter [Django-doc] . The related_name specifies the name of the relation in reverse so from Course to Profile in this case. It thus should be something like 'profiles' :

class Profile(AbstractUser):
    bio = models.TextField()
    image = models.ImageField(default='defaults/user/default_u_i.png', 
    courses = models.ManyToManyField('home.Course')

    def __str__(self):
        return self.username

You thus can obtain the people that particiate in a Course object with:

mycourse

and you can access the courses in which a Profile is enrolled with:

myprofile

For more information, see the Many-to-many relationships section of the documentation .

You can add a course to the courses of a user with:

@login_required
def course_add(request):
    if request.method == 'POST':
        form = CourseForm(request.POST)
        if form.is_valid():
            course = form.save()
            request.user
    else:
        form = CourseForm()
    context = {
        'form': form
    }
    return render(request,'home/courses/course_add.html', context)

Answer 2

You don't need to add the related name. Default is "courses_set" in your case. Here is excerpt from: https://docs.djangoproject.com/en/dev/topics/db/queries/#backwards-related-objects

Following relationships “backward” If a model has a ForeignKey, instances of the foreign-key model will have access to a Manager that returns all instances of the first model. By default, this Manager is named FOO_set, where FOO is the source model name, lowercased. This Manager returns QuerySets, which can be filtered and manipulated as described in the “Retrieving objects” section above.