Lesson 3: Django Apps

📘 Lesson 3: Django Apps

🔰 Introduction

In Django, a project is the whole website — but the real power comes from apps.
Each feature inside a Django project is built as a separate app so your project stays clean, organized, and professional just like modern company websites.

Examples of apps:

• blog
• accounts (login system)
• store
• api
• poems (for your future poetry system)

By the end of this lesson, you will:
✔ Understand what an app is
✔ Create your first Django app
✔ Install the app inside settings.py
✔ Build the foundation for your project’s future apps
✔ Be ready for the homework: create a blog app

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🧩 1. What is a Django App?

A Django app is:

• A module inside your project
• Responsible for doing one job
• Reusable (you can copy it into another project)
• Easy to maintain

Think of a Django project like a company building:

Floor	Purpose
Project	Entire building
App	A department (HR, IT, Finance)

Each department does one job.
Each app does one job.

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🏗 2. Creating New App

Make sure your virtual environment is active:

source venv/bin/activate

Go inside your Django project directory (where manage.py is):

cd hello_django

Create your new app:

python manage.py startapp home

You will now see this new folder:

home/
    admin.py
    apps.py
    models.py
    views.py
    urls.py (you will create this)

This app is now part of your project — but Django does not use it yet.

You must install it.

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⚙️ 3. Installing the App in settings.py

Open:

hello_django/config/settings.py

Find the INSTALLED_APPS section.

Add your app:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'core',
    'home', # Your apps
]

That’s it — your app is now registered!

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🌐 4. Creating the New App View

Inside home/views.py:

from django.http import HttpResponse

def homepage(request):
    return HttpResponse("Welcome to my first Django app!")

Now create a urls.py file inside the app:

home/urls.py

Add this:

from django.urls import path
from . import views

urlpatterns = [
    path('', views.homepage, name='homepage'),
]

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🔗 5. Include App URLs in Project URLs

Open:

hello_django/config/urls.py

Update to:

from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('admin/', admin.site.urls),
    path('core/', include('core.urls')),  
    path('', include('home.urls')),
]

Now visit:

run the server: 
python manage.py runserver 0.0.0.0:8011

then visit:
http://your-server-ip:8011/

You should see:

“Welcome to my first Django app!”

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🚨 Beginners Troubleshooting

❗ “ModuleNotFoundError: No module named ‘home’”

You created the app outside the project folder.
Make sure home/ is next to manage.py.

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❗ “TemplateDoesNotExist”

You added templates before creating the templates folder.
We will fix this in Lesson 6.

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❗ Running server on busy port

Use a different port:

python manage.py runserver 0.0.0.0:8011

(We use 8011 in all lessons to avoid conflicts)

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📝 Homework

Create a new app called blog

Your task:

1. Create the app python manage.py startapp blog
2. Add it to INSTALLED_APPS
3. Create a view:
   Inside blog/views.py def blog_home(request): return HttpResponse("This is the blog homepage.")
4. Create urls.py for the app
5. Include it in project urls.py at: /blog/

Example:

http://your-server-ip:8011/blog/

It should display:

This is the blog homepage.

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