Question

I have four models in my models.py which are:

models.py

class Course(models.Model):
    course_code = models.CharField(max_length=100,unique=True)
    title = models.CharField(max_length=200)
    short = models.CharField(max_length=50)
    elective_group = models.CharField(max_length=100)

class Unit(models.Model):
    title = models.CharField(max_length=100)
    short = models.CharField(max_length=50)
    course = models.ForeignKey(Course)

class Pattern(models.Model):
    pattern_name = models.CharField(max_length=200)

class ExamSchedule(models.Model):
    exam_date = models.DateTimeField()
    course = models.ForeignKey(Course)
    pattern = models.ForeignKey(Pattern)
    units = models.ManyToManyField(Units)

I have all these models register with admin site, so that i can use admin functionality for these models.

My problem is when a user creates or edits a ExamSchedule object , i want the units(field) multivalue widget should contains only those values that are associated with a course as every course can have multiple units. So if user creates an Examschedule object and after selecting a course from dropdown the unit widget should only contains those units that related to the course selected.

Django-Smart-Select could have been useful but it only supports foreign key chained and grouped selects nor ManyToManyField chained select.

Thanks

Answer 1

You can send the selected course with a Ajax request and do this to get the related units.
Lets say you select communication networks (cn) as the course you can get the related units like so:

cn_units = Unit.object.filter(course = 'cn').values_list('id',flat=True)

This will return a single list of all the related units to that course.
You can send this list as a response to your ajax request, iterate over this list and populate the select box for unit in ExamSchedule form. I consider plain ajax because its very flexible.