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Backend Development

2. CRUD

Django provides an Object-Relational Mapper (ORM) that allows us to perform CRUD (Create, Read, Update, Delete) operations on database models easily.

1. Create (Insert Data)

You can insert data using:

  • .save()
  • .create()
  • .bulk_create()

Using .save()

from myapp.models import Post


post = Post(title="New Post", content="This is a new blog post.")
post.save()  # Saves data to the database

Using .create()

Post.objects.create(title="Another Post", content="Created using create()")

Using .bulk_create() (Multiple Inserts)

Post.objects.bulk_create([
    Post(title="Post 1", content="Content 1"),
    Post(title="Post 2", content="Content 2"),
])

2. Read (Retrieve Data)

You can retrieve data using:

  • .all()
  • .filter()
  • .get()
  • .values()
  • .count()

Retrieve All Objects

posts = Post.objects.all()
for post in posts:
    print(post.title, post.content)

Retrieve a Single Object

post = Post.objects.get(id=1)  # Get the post with ID = 1
print(post.title)

⚠️ .get() raises an error if no object is found.

Filter Data (Retrieve Specific Records)

posts = Post.objects.filter(title="New Post")  # Filter by title

Retrieve Specific Fields Only

posts = Post.objects.values('title', 'content')  # Returns a dictionary-like QuerySet

Count Records

count = Post.objects.count()  # Count total number of records

3. Update (Modify Existing Data)

You can update data using:

  • Modify an object and call .save()
  • Use .update() for multiple records

Update a Single Object

post = Post.objects.get(id=1)
post.title = "Updated Title"
post.save()

Update Multiple Records at Once

Post.objects.filter(title="Old Title").update(title="New Title")

4. Delete (Remove Data)

You can delete data using:

  • .delete()
  • .filter().delete() for multiple records

Delete a Single Object

post = Post.objects.get(id=1)
post.delete()

Delete Multiple Objects

Post.objects.filter(title="Old Title").delete()

Delete All Objects in a Model

Post.objects.all().delete()

5. Full CRUD Example

5.1 View for CRUD

views.py
from django.shortcuts import render, get_object_or_404, redirect
from .models import Post
from .forms import PostForm


# Create a new post
def create_post(request):
    if request.method == 'POST':
        form = PostForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('post_list')  # Redirect to post list
    else:
        form = PostForm()
    return render(request, 'blog/create_post.html', {'form': form})


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


# Update a post
def update_post(request, post_id):
    post = get_object_or_404(Post, id=post_id)
    if request.method == 'POST':
        form = PostForm(request.POST, instance=post)
        if form.is_valid():
            form.save()
            return redirect('post_list')
    else:
        form = PostForm(instance=post)
    return render(request, 'blog/update_post.html', {'form': form})


# Delete a post
def delete_post(request, post_id):
    post = get_object_or_404(Post, id=post_id)
    if request.method == 'POST':
        post.delete()
        return redirect('post_list')
    return render(request, 'blog/delete_post.html', {'post': post})

5.2 CRUD Templates

Form for Creating and Updating Posts

create_post.html, update_post.html
<form method="post">
    {% csrf_token %}
    {{ form.as_p }}
    <button type="submit">Submit</button>
</form>

List All Posts

post_list.html
{% for post in posts %}
    <h2>{{ post.title }}</h2>
    <p>{{ post.content }}</p>
    <a href="{% url 'update_post' post.id %}">Edit</a>
    <a href="{% url 'delete_post' post.id %}">Delete</a>
{% endfor %}

Delete Confirmation

delete_post.html
<form method="post">
    {% csrf_token %}
    <p>Are you sure you want to delete "{{ post.title }}"?</p>
    <button type="submit">Yes, Delete</button>
</form>

5.3 CRUD URLs

urls.py
from django.urls import path
from .views import create_post, post_list, update_post, delete_post


urlpatterns = [
    path('', post_list, name='post_list'),
    path('create/', create_post, name='create_post'),
    path('update/<int:post_id>/', update_post, name='update_post'),
    path('delete/<int:post_id>/', delete_post, name='delete_post'),
]