Login view and template in Django - Mini Project: Build & Apply

Login view and template

📖 Scenario: You are building a simple login page for a website. Users will enter their username and password to access their account.

🎯 Goal: Create a Django view to handle user login and a corresponding HTML template with a form for username and password.

📋 What You'll Learn

Create a Django view function named login_view that uses django.contrib.auth.authenticate and django.contrib.auth.login to log in users.

Create an HTML template named login.html with a form containing username and password input fields and a submit button.

The form should use the POST method and submit to the same URL.

If authentication fails, the view should re-render the template with an error message.

💡 Why This Matters

🌍 Real World

Login pages are essential for websites that require user accounts, such as social media, e-commerce, or online services.

💼 Career

Understanding how to implement user authentication is a key skill for web developers working with Django or similar frameworks.

1

Create the login view function

Create a Django view function called login_view that accepts a request parameter and imports authenticate and login from django.contrib.auth. For now, just return render(request, 'login.html').

Django

# Your code here

Hint

Start by importing authenticate and login from django.contrib.auth. Then define login_view that returns render(request, 'login.html').

2

Add POST check and get username and password

Inside the login_view function, add a check for request.method == 'POST'. If true, get username and password from request.POST using request.POST.get('username') and request.POST.get('password').

Django

from django.shortcuts import render
from django.contrib.auth import authenticate, login

def login_view(request):
    if request.method == 'POST':
        # Get username and password from request.POST
        # Your code here
    return render(request, 'login.html')

Hint

Use request.method == 'POST' to check the form submission. Then get the username and password from request.POST.

3

Authenticate user and login or show error

Still inside the POST check, use authenticate(request, username=username, password=password) to verify credentials. If the user is valid, call login(request, user) and redirect to '/'. Otherwise, set an error variable to 'Invalid username or password' and pass it to the template context.

Django

from django.shortcuts import render
from django.contrib.auth import authenticate, login
from django.shortcuts import redirect

def login_view(request):
    if request.method == 'POST':
        username = request.POST.get('username')
        password = request.POST.get('password')
        # Authenticate user and login or set error
        # Your code here
    return render(request, 'login.html')

Hint

Use authenticate to check credentials. If valid, call login and redirect. Otherwise, prepare an error message for the template.

4

Create the login.html template with form and error display

Create an HTML file named login.html with a form that uses method='post'. Include {% csrf_token %} inside the form. Add input fields with name='username' and name='password'. Add a submit button with text 'Login'. Below the form, display the error variable if it exists inside a <p> tag with style='color: red;'.

Django

from django.shortcuts import render
from django.contrib.auth import authenticate, login
from django.shortcuts import redirect

def login_view(request):
    error = None
    if request.method == 'POST':
        username = request.POST.get('username')
        password = request.POST.get('password')
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            return redirect('/')
        else:
            error = 'Invalid username or password'
    return render(request, 'login.html', {'error': error})

Hint

Create a form with POST method, include {% csrf_token %}, username and password inputs, and a submit button. Show the error message in red if it exists.

Practice

1. What is the main purpose of Django's LoginView?

easy

A. To display a list of logged-in users

B. To create a new user registration form

C. To handle password reset requests

D. To provide a ready-made view for user login handling

Solution

1. Step 1: Understand Django's built-in views

   Django provides LoginView as a built-in class-based view to handle user login functionality easily.

2. Step 2: Identify the purpose of LoginView

   It manages displaying the login form, validating user credentials, and logging users in.

3. Final Answer:

   To provide a ready-made view for user login handling -> Option D

4. Quick Check:

   LoginView = ready-made login handler [OK]

Hint: LoginView is for login pages, not registration or reset [OK]

Common Mistakes:

• Confusing LoginView with registration or password reset views
• Thinking LoginView lists users
• Assuming LoginView creates new users

2. Which of the following is the correct way to specify a custom template for Django's LoginView?

easy

A. template = 'login.html'

B. template_name = 'login.html'

C. templateFile = 'login.html'

D. templatePath = 'login.html'

Solution

1. Step 1: Recall Django's class-based view attribute for templates

   Django's class-based views use the attribute template_name to specify the HTML template file.

2. Step 2: Match the correct attribute name

   Among the options, only template_name is the correct attribute to set the template.

3. Final Answer:

   template_name = 'login.html' -> Option B

4. Quick Check:

   Use template_name to set template in CBVs [OK]

Hint: Remember: class-based views use template_name, not template [OK]

Common Mistakes:

• Using 'template' instead of 'template_name'
• Using camelCase like 'templateFile' or 'templatePath'
• Forgetting to set template_name at all

3. Given this simple login template snippet:

<form method="post">
  {% csrf_token %}
  {{ form.as_p }}
  <button type="submit">Login</button>
</form>

What will happen if the {% csrf_token %} tag is removed?

medium

A. The form will submit successfully without any issues

B. The form will submit but the user will not be logged in

C. Django will raise a CSRF verification failed error on form submission

D. The form will redirect to the homepage automatically

Solution

1. Step 1: Understand CSRF protection in Django forms

   Django requires a CSRF token in POST forms to protect against cross-site request forgery attacks.

2. Step 2: Effect of removing the CSRF token

   If the {% csrf_token %} tag is missing, Django will reject the POST request with a CSRF verification error.

3. Final Answer:

   Django will raise a CSRF verification failed error on form submission -> Option C

4. Quick Check:

   Missing csrf_token causes CSRF error [OK]

Hint: Always include {% csrf_token %} in POST forms [OK]

Common Mistakes:

• Assuming form submits without CSRF token
• Thinking user won't log in but no error occurs
• Believing form redirects automatically without token

4. You wrote this URL pattern for login:

path('login/', LoginView.as_view(template_name='login.html'))

But when you visit /login/, you get a TemplateDoesNotExist error. What is the most likely cause?

medium

A. The template file 'login.html' is missing or not in the correct templates directory

B. You forgot to import LoginView from django.contrib.auth.views

C. You need to add a trailing slash in the URL pattern

D. The URL pattern should be named 'login_view' instead of 'login/'

Solution

1. Step 1: Understand TemplateDoesNotExist error

   This error means Django cannot find the specified template file in any of the configured template directories.

2. Step 2: Check common causes

   Since the URL pattern and import are likely correct, the most common cause is the missing or misplaced template file.

3. Final Answer:

   The template file 'login.html' is missing or not in the correct templates directory -> Option A

4. Quick Check:

   TemplateDoesNotExist = missing or misplaced template [OK]

Hint: Check template file location if TemplateDoesNotExist error appears [OK]

Common Mistakes:

• Assuming import errors cause TemplateDoesNotExist
• Thinking URL pattern naming affects template loading
• Ignoring template directory settings

5. You want to customize the login form to add a 'Remember Me' checkbox that keeps users logged in longer. Which approach correctly integrates this feature using Django's LoginView?

hard

A. Override LoginView to add a custom form with a 'remember_me' field and adjust session expiry in form_valid

B. Add a checkbox in the template only; Django handles session duration automatically

C. Set template_name to a new template with the checkbox but do not change the view or form

D. Use Django's default LoginView without changes; 'Remember Me' is built-in

Solution

1. Step 1: Understand customizing LoginView

   To add new fields like 'Remember Me', you must create a custom form and override LoginView to use it.

2. Step 2: Adjust session expiry based on 'remember_me'

   Override form_valid method to set session expiry longer if 'remember_me' is checked.

3. Final Answer:

   Override LoginView to add a custom form with a 'remember_me' field and adjust session expiry in form_valid -> Option A

4. Quick Check:

   Custom form + override form_valid for 'Remember Me' [OK]

Hint: Customize form and override form_valid to handle 'Remember Me' [OK]

Common Mistakes:

• Adding checkbox only in template without backend logic
• Assuming default LoginView supports 'Remember Me' automatically
• Not overriding form_valid to change session expiry