Django Core Concepts

MVT Architecture

class Article(models.Model):
    title = models.CharField()

def article_list(request):
    articles = Article.objects.all()

<h1>{{ article.title }}</h1>

path('articles/', article_list)

🔹 Models - Data Layer

Models represent your database tables as Python classes. Each model maps to a single database table and defines the structure and behavior of your data.

# blog/models.py
from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField()
    
    def __str__(self):
        return self.name

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    published_date = models.DateTimeField(auto_now_add=True)
    
    def __str__(self):
        return self.title

🔹 Views - Logic Layer

Views receive web requests and return web responses. They contain the business logic that processes data from models and passes it to templates.

🔸 Function-Based Views

# blog/views.py
from django.shortcuts import render, get_object_or_404
from .models import Post

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

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post': post})

🔸 Class-Based Views

# blog/views.py
from django.views.generic import ListView, DetailView
from .models import Post

class PostListView(ListView):
    model = Post
    template_name = 'blog/post_list.html'
    context_object_name = 'posts'
    ordering = ['-published_date']

class PostDetailView(DetailView):
    model = Post
    template_name = 'blog/post_detail.html'

🔹 Templates - Presentation Layer

Templates are HTML files with Django template language syntax. They display data passed from views and support logic like loops and conditionals.

<!-- templates/blog/post_list.html -->
{% extends 'base.html' %}

{% block title %}Blog Posts{% endblock %}

{% block content %}
    <h1>All Blog Posts</h1>
    
    {% if posts %}
        {% for post in posts %}
            <article>
                <h2>{{ post.title }}</h2>
                <p>By {{ post.author.name }} on {{ post.published_date|date:"F d, Y" }}</p>
                <p>{{ post.content|truncatewords:30 }}</p>
                <a href="{% url 'post_detail' post.pk %}">Read More</a>
            </article>
        {% endfor %}
    {% else %}
        <p>No posts available.</p>
    {% endif %}
{% endblock %}

🔹 URL Routing

Django's URL dispatcher maps URL patterns to views. It determines which view function handles each incoming request based on the URL path.

# blog/urls.py
from django.urls import path
from . import views

urlpatterns = [
    path('', views.post_list, name='post_list'),
    path('post/<int:pk>/', views.post_detail, name='post_detail'),
]

# mysite/urls.py
from django.contrib import admin
from django.urls import path, include

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

🔹 Django ORM (Object-Relational Mapping)

Django's ORM lets you interact with databases using Python code instead of SQL. It translates Python operations into database queries automatically.

# Query examples
from blog.models import Post, Author

# Create
post = Post.objects.create(
    title="My First Post",
    content="Hello World!",
    author=author
)

# Read
all_posts = Post.objects.all()
recent_posts = Post.objects.filter(published_date__year=2024)
single_post = Post.objects.get(pk=1)

# Update
post.title = "Updated Title"
post.save()

# Delete
post.delete()

🔹 Django Admin Interface

Django provides a built-in admin interface for managing your data. Register your models to make them editable through the admin panel.

# blog/admin.py
from django.contrib import admin
from .models import Post, Author

@admin.register(Post)
class PostAdmin(admin.ModelAdmin):
    list_display = ['title', 'author', 'published_date']
    list_filter = ['published_date', 'author']
    search_fields = ['title', 'content']

admin.site.register(Author)

# Create admin user
python manage.py createsuperuser

🔹 Request-Response Cycle

Understanding how Django processes requests helps you build better applications:

# Complete example
# 1. URL matches pattern
path('posts/', views.post_list)

# 2. View processes request
def post_list(request):
    posts = Post.objects.all()  # Get data from model
    return render(request, 'blog/post_list.html', {'posts': posts})

# 3. Template renders
# {{ post.title }} displays each post