Notes

-------------------------------------------------------------------------[Day 1]--------------------------------------------------------------------------

🚀 DJANGO BACKEND NOTES (Lesson 1–17)

---

1️⃣ What is Backend?

• Backend = brain of website 🧠
• It is not visible to users
• It:
  • Receives requests
  • Processes logic
  • Talks to database
  • Sends response

Flow:

Browser → Backend → Database → Backend → Browser

---

2️⃣ What is Django?

• Django = Python backend framework
• Tool to build backend faster
• Handles:
  • Security
  • URLs
  • Database connection
  • Admin panel

Django saves time and prevents common mistakes.

---

3️⃣ What is a Django Project?

• Project = big container 📦
• One website = one project
• Holds:
  • Settings
  • URLs
  • Apps

Created using:

django-admin startproject mysite

---

4️⃣ Running the Server

Server = program that listens 👂

Run server:

python manage.py runserver

Open:

http://127.0.0.1:8000/

127.0.0.1 = your computer 8000 = port (door number)

---

5️⃣ What is a Django App?

• App = small worker inside project 👷
• Each app does one job
• Example:
  • Blog app
  • Payment app
  • Auth app

Create app:

python manage.py startapp blog

---

6️⃣ Registering an App

Add app to settings.py:

INSTALLED_APPS = [
    ...
    'blog',
]

Without registration:

• Django ignores app ❌

---

7️⃣ What is a View?

View = function that:

• Receives request
• Runs logic
• Returns response

Example:

from django.http import HttpResponse

def hello(request):
    return HttpResponse("Hello")

---

8️⃣ URLs (Routing)

URL connects path → view

In urls.py:

from blog.views import hello

urlpatterns = [
    path('hello/', hello),
]

Flow:

URL → View → Response

---

9️⃣ Templates

Template = HTML page 🖼️ Used to send proper web pages.

In view:

return render(request, 'blog/hello.html')

Browser only sees HTML.

---

🔟 Passing Data to Template

Send dictionary:

data = {"name": "Dev"}
return render(request, 'blog/hello.html', data)

In template:

{{ name }}

View sends data. Template shows data.

---

1️⃣1️⃣ Template Logic (if & for)

Conditional:

{% if is_logged_in %} Welcome {% endif %}

Loop:

{% for item in items %} {{ item }} {% endfor %}

Template has small logic only.

---

1️⃣2️⃣ Models (Database Blueprint)

Model = table blueprint 📊

Example:

class Post(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

Create table:

python manage.py makemigrations
python manage.py migrate

Model = permanent storage 💾

---

1️⃣3️⃣ Admin Panel

Admin = control room 🎛️

Create superuser:

python manage.py createsuperuser

Register model:

from .models import Post
admin.site.register(Post)

Open:

/admin/

---

1️⃣4️⃣ Showing Database Data

Fetch in view:

posts = Post.objects.all()
return render(request, 'blog/post_list.html', {"posts": posts})

In template:

{% for post in posts %} {{ post.title }} {% endfor %}

Flow:

Model → View → Template

---

1️⃣5️⃣ Manual Forms

HTML form:

<form method="post">
  {% csrf_token %}
  <input name="title" />
</form>

In view:

if request.method == "POST":
    title = request.POST.get("title")
    Post.objects.create(title=title)

POST = sending data GET = asking for page

---

1️⃣6️⃣ Django Forms (ModelForm)

Create forms.py:

class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        fields = ['title', 'content']

In view:

form = PostForm(request.POST)
if form.is_valid():
    form.save()

Template:

{{ form.as_p }}

Django handles:

• Validation
• Saving
• Error messages

---

1️⃣7️⃣ App-Level URLs (Clean Structure)

Create:

blog/urls.py

from django.urls import path
from .views import post_list

urlpatterns = [
    path('', post_list),
]

Project urls.py:

path('posts/', include('blog.urls')),

Project = main gate App = internal roads

---

🧠 Core Backend Flow (Important)

Always remember:

Request
   ↓
URL
   ↓
View
   ↓
Model (optional)
   ↓
Template
   ↓
Response

That is Django’s heart ❤️