Our e-learning platform will offer courses on various subjects. Each course will be divided into a configurable number of modules, and each module will contain a configurable number of contents. There will be contents of various types: text, file, image, or video. The following example shows what the data structure of our course catalog will look like:

Subject 1
  Course 1
    Module 1
      Content 1 (image)
      Content 2 (text)
    Module 2
      Content 3 (text)
      Content 4 (file)
      Content 5 (video)
      ...

Let's build the course models. Edit the models.py file of the courses application and add the following code to it:

from django.db import models
from django.contrib.auth.models import User

class Subject(models.Model):
    title = models.CharField(max_length=200)
    slug = models.SlugField(max_length=200, unique=True)

    class Meta:
        ordering = ['title']

    def __str__(self):
        return self.title

class Course(models.Model):
    owner = models.ForeignKey(User,
                              related_name='courses_created',
                              on_delete=models.CASCADE)
    subject = models.ForeignKey(Subject,
                                related_name='courses',
                                on_delete=models.CASCADE)
    title = models.CharField(max_length=200)
    slug = models.SlugField(max_length=200, unique=True)
    overview = models.TextField()
    created = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['-created']

    def __str__(self):
        return self.title


class Module(models.Model):
    course = models.ForeignKey(Course,
                               related_name='modules',
                               on_delete=models.CASCADE)
    title = models.CharField(max_length=200)
    description = models.TextField(blank=True)

    def __str__(self):
        return self.title

These are the initial Subject, Course, and Module models. The Course model fields are as follows:

• owner: The instructor that created this course.
• subject: The subject that this course belongs to. A ForeignKey field that points to the Subject model.
• title: The title of the course.
• slug: The slug of the course. This will be used in URLs later.
• overview: This is a TextField column to include an overview of the course.
• created: The date and time when the course was created. It will be automatically set by Django when creating new objects because of auto_now_add=True.

Each course is divided into several modules. Therefore, the Module model contains a ForeignKey field that points to the Course model.

Open the shell and run the following command to create the initial migration for this app:

python manage.py makemigrations

You will see the following output:

Migrations for 'courses':
  0001_initial.py:
    - Create model Course
    - Create model Module
    - Create model Subject
    - Add field subject to course

Then, run the following command to apply all migrations to the database:

python manage.py migrate

You should see output including all applied migrations, including those of Django. The output will contain the following line:

Applying courses.0001_initial... OK

The models of our courses app have been synced to the database.