I ran across an issue today that, in hindsight, was simple and probably a result of not reading the Django documentation thoroughly enough. I'm definitely still in the "learning" phase of my relationship with Django.
Consider this (imperfect) example: you're using a ModelForm to allow users of your web app to create a Student. The user would supply the student's name, date of birth, and address in a form, but the student ID should be generated based on their other information (e.g. name and date of birth).
The ModelForm object won't give you access to the underlying Model's student_id field unless you include it with the form, which is undesirable. You could also save the Student to the database, then update its student_id field, but that's pretty inefficient. The better solution:
# Model
class Student(models.Model):
student_id = models.CharField()
name = models.CharField()
dob = models.DateField()
address = models.CharField()
# ModelForm
class AddStudentForm(forms.ModelForm):
class Meta:
model = Student
# don't include student_id
fields = ['name', 'birthday', 'address']
# View
def add_student(request):
...
if form.is_valid():
# this will gave you an instance of the Student model without saving it to the db
student = form.save(commit=False)
# then you can create the student_id and save to the db
student.student_id = create_id(student.name, student.dob)
student.save()
....