Handling two Django models in a single POST

There are times when, you want to handle multiple Django models in a single POST request (By this i meant data posted from html form/ template contains data of two different Django models). I was struggling with this few months back and got a fantastic reference link from #django on IRC.

You can use the below method as a simple example, here’s a view that updates a User and their Profile in one view:

def user_edit(request):
    if request.method == 'POST':
        user_form = UserForm(request.POST, instance=request.user)
        profile_form = ProfileForm(request.POST, instance=request.user.profile)

        if all([user_form.is_valid(), profile_form.is_valid()]):
            user = user_form.save()
            profile = profile_form.save()
            return redirect(user)
    else:
        user_form = UserForm(instance=request.user)
        profile_form = ProfileForm(instance=request.user.profile)

    return render(request, 'user_form.html', {
            'user_form': user_form,
            'profile_form': profile_form,
            })

The two most important things to notice here are:

a. The use of all() instead of user_form.is_valid() and profile_form.is_valid().

This is because Python will skip the if clause if the first form is not valid, and so it won’t run validation on the second form. If some error is present in second from user will again get the error second time. using all() runs validation on all the submitted forms thus you get the errors at one time.

b. Two forms in the context.

Just render them all inside the one <form> tag, and it will be fine. If any of the field names clash, pass a prefix= when constructing one of the forms, to prefix its field names so they’re unique.

Related blogs :

  1. Django – AttributeError: ‘Http404’ object has no attribute ‘status_code’
  2. Make primary key with two or more field in Django

Make primary key with two or more field in Django

Most of the time, people don’t actually need their composite (multi-column) key to be the primary key.

Django operates best with surrogate keys –  that is, it automatically defines an autoincrement field called id and sets that to be the primary key. That is suitable for almost all the users.

If you then need to enforce a unique constraint on your model across two or more fields, you can use the unique_together setting in the inner Meta class.

class Student(models.Model):
    Name = models.CharField(max_length=100)
    Roll = models.CharField(max_length=20)
    Department = models.CharField(max_length=15)

    class Meta:
        unique_together = (('Roll', 'Department'),)

It would act as a surrogate primary key column.

Sets of field names that, taken together, must be unique:

unique_together = (('Roll', 'Department'),)

This is a tuple of tuples that must be unique when considered together. It’s used in the Django admin and is enforced at the database level (i.e., the appropriate UNIQUE statements are included in the CREATE TABLE statement).

For convenience, unique_together can be a single tuple when dealing with a single set of fields :

unique_together = ('Roll', 'Department')

Count and group by equivalent in Django Queryset

While working on a Django project, I came through a problem. I wanted to select  a column & count of that column group by that column from a table. (categoryname & count  of items for each category), so in simple SQL it would be as simple as this:

SELECT column_name , COUNT(column_name) FROM TableName GROUP BY column_name;

Now Django Sub Query for the following given SQL code would be.


data = MyModel.objects.filter(column_1_gt = 'some value').values('column_name').order_by().annotate(Count('column_name'))

  • values(‘column_name) –  for inclusion only player_type field into GROUP BY clause.
  • order_by() – for exclusion possible default ordering that can cause not needed fields inclusion in SELECT and GROUP BY.