Bài 16: Messages Framework

Messages Framework Là Gì?

Django Messages Framework cho phép hiển thị one-time notifications cho users (flash messages).

# Common use cases:# - "Login successful"# - "Product added to cart"# - "Form submitted successfully"# - "Error: Invalid data"# - "Warning: This action cannot be undone" # settings.py - Already enabled by defaultINSTALLED_APPS = [    'django.contrib.messages',  # Messages framework    # ...] MIDDLEWARE = [    'django.contrib.sessions.middleware.SessionMiddleware',    'django.contrib.messages.middleware.MessageMiddleware',    # ...] # Messages stored in session, displayed once, then deletedfrom django.contrib import messages def my_view(request):    messages.success(request, 'Operation completed successfully!')    return redirect('home') # In template:{% if messages %}    {% for message in messages %}        <div class="alert alert-{{ message.tags }}">            {{ message }}        </div>    {% endfor %}{% endif %}

How Messages Work

# Flow:# 1. View adds message to queue# 2. Message stored in session# 3. Template displays message# 4. Message automatically deleted after display # Example flow:def create_post(request):    if request.method == 'POST':        form = PostForm(request.POST)        if form.is_valid():            post = form.save()            # Add success message            messages.success(request, 'Post created successfully!')            return redirect('post_detail', pk=post.pk)        else:            # Add error message            messages.error(request, 'Please correct the errors below.')        return render(request, 'create_post.html', {'form': form}) # Template automatically displays and clears message

Message Levels

Built-in Levels

from django.contrib import messages # DEBUG (10) - Development-related messagesmessages.debug(request, 'SQL query executed: SELECT * FROM posts') # INFO (20) - Informational messagesmessages.info(request, 'Your profile was viewed 10 times today') # SUCCESS (25) - Success confirmationsmessages.success(request, 'Your post has been published!') # WARNING (30) - Warning messagesmessages.warning(request, 'Your subscription expires in 3 days') # ERROR (40) - Error messagesmessages.error(request, 'Failed to upload file. File too large.') # Level constantsfrom django.contrib.messages import constants as message_constantsprint(message_constants.DEBUG)    # 10print(message_constants.INFO)     # 20print(message_constants.SUCCESS)  # 25print(message_constants.WARNING)  # 30print(message_constants.ERROR)    # 40

Setting Message Level

# settings.py - Set minimum level to displayfrom django.contrib.messages import constants as messages MESSAGE_LEVEL = messages.DEBUG  # Show all messages# MESSAGE_LEVEL = messages.INFO    # Hide DEBUG messages# MESSAGE_LEVEL = messages.WARNING # Only WARNING and ERROR # Change level per-requestfrom django.contrib import messages def debug_view(request):    # Show all messages for this request    messages.set_level(request, messages.DEBUG)        messages.debug(request, 'Debug info')    messages.info(request, 'Info message')        return render(request, 'debug.html') # Get current leveldef view(request):    current_level = messages.get_level(request)    print(f"Current message level: {current_level}")

Custom Message Levels

# Define custom levelsfrom django.contrib.messages import constants as messages CRITICAL = 50 # Add custom messagefrom django.contrib import messages def add_custom_message(request):    messages.add_message(        request,         CRITICAL,  # Custom level        'Critical error occurred!',        extra_tags='critical'    ) # settings.py - Add custom level tagMESSAGE_TAGS = {    messages.DEBUG: 'debug',    messages.INFO: 'info',    messages.SUCCESS: 'success',    messages.WARNING: 'warning',    messages.ERROR: 'danger',    50: 'critical',  # Custom level}

Adding Messages

Basic Message Methods

from django.contrib import messages def view_examples(request):    # Success message    messages.success(request, 'Changes saved successfully!')        # Info message    messages.info(request, 'You have 3 new notifications')        # Warning message    messages.warning(request, 'Your password will expire soon')        # Error message    messages.error(request, 'Failed to process payment')        # Debug message    messages.debug(request, 'Query took 0.5 seconds')        return redirect('home')

Messages with Extra Tags

# Add custom CSS classesmessages.success(    request,    'Profile updated!',    extra_tags='profile-update dismissible') # Add failure levelmessages.error(    request,    'Database connection failed',    extra_tags='database-error critical',    fail_silently=False) # Generic add_messagefrom django.contrib.messages import constants messages.add_message(    request,    constants.SUCCESS,    'Operation completed',    extra_tags='custom-class',    fail_silently=True)

Conditional Messages

def update_profile(request):    if request.method == 'POST':        form = ProfileForm(request.POST, instance=request.user.profile)                if form.is_valid():            form.save()                        # Success message            messages.success(request, 'Profile updated successfully!')                        # Additional info based on changes            if form.cleaned_data.get('newsletter'):                messages.info(                    request,                    'You are now subscribed to our newsletter'                )                        return redirect('profile')        else:            # Error message with field info            error_fields = ', '.join(form.errors.keys())            messages.error(                request,                f'Please correct errors in: {error_fields}'            )        return render(request, 'edit_profile.html', {'form': form})

Multiple Messages

def process_bulk_action(request):    selected_ids = request.POST.getlist('selected')        success_count = 0    error_count = 0        for item_id in selected_ids:        try:            process_item(item_id)            success_count += 1        except Exception as e:            error_count += 1        # Add summary messages    if success_count:        messages.success(            request,            f'{success_count} items processed successfully'        )        if error_count:        messages.error(            request,            f'{error_count} items failed to process'        )        return redirect('item_list')

Displaying Messages

Basic Template Display

<!-- Base template: templates/base.html --><!DOCTYPE html><html><head>    <title>{% block title %}My Site{% endblock %}</title>    <style>        .messages {            list-style: none;            padding: 0;        }        .message {            padding: 10px;            margin: 10px 0;            border-radius: 4px;        }        .message.success {            background-color: #d4edda;            color: #155724;        }        .message.error {            background-color: #f8d7da;            color: #721c24;        }        .message.warning {            background-color: #fff3cd;            color: #856404;        }        .message.info {            background-color: #d1ecf1;            color: #0c5460;        }    </style></head><body>    <!-- Messages section -->    {% if messages %}        <ul class="messages">            {% for message in messages %}                <li class="message {{ message.tags }}">                    {{ message }}                </li>            {% endfor %}        </ul>    {% endif %}        <!-- Page content -->    {% block content %}    {% endblock %}</body></html>

Bootstrap Styled Messages

<!-- Using Bootstrap 5 -->{% if messages %}    <div class="container mt-3">        {% for message in messages %}            <div class="alert alert-{{ message.tags }} alert-dismissible fade show" role="alert">                {{ message }}                <button type="button" class="btn-close" data-bs-dismiss="alert"></button>            </div>        {% endfor %}    </div>{% endif %} <!-- Map Django tags to Bootstrap classes --><!-- settings.py -->from django.contrib.messages import constants as messages MESSAGE_TAGS = {    messages.DEBUG: 'secondary',    messages.INFO: 'info',    messages.SUCCESS: 'success',    messages.WARNING: 'warning',    messages.ERROR: 'danger',}

Custom Message Display

<!-- With icons -->{% if messages %}    {% for message in messages %}        <div class="alert alert-{{ message.tags }}">            {% if message.level == DEFAULT_MESSAGE_LEVELS.ERROR %}                <i class="fa fa-times-circle"></i>            {% elif message.level == DEFAULT_MESSAGE_LEVELS.SUCCESS %}                <i class="fa fa-check-circle"></i>            {% elif message.level == DEFAULT_MESSAGE_LEVELS.WARNING %}                <i class="fa fa-exclamation-triangle"></i>            {% else %}                <i class="fa fa-info-circle"></i>            {% endif %}            {{ message }}        </div>    {% endfor %}{% endif %} <!-- With close button and fade effect -->{% if messages %}    {% for message in messages %}        <div class="message-box message-{{ message.tags }}" data-message-id="{{ forloop.counter }}">            <span class="message-text">{{ message }}</span>            <button class="close-btn" onclick="closeMessage({{ forloop.counter }})">                &times;            </button>        </div>    {% endfor %}{% endif %} <script>function closeMessage(id) {    const element = document.querySelector(`[data-message-id="${id}"]`);    element.style.opacity = '0';    setTimeout(() => element.remove(), 300);} // Auto-dismiss after 5 secondsdocument.querySelectorAll('.message-box').forEach(box => {    setTimeout(() => {        box.style.opacity = '0';        setTimeout(() => box.remove(), 300);    }, 5000);});</script>

Accessing Message Properties

{% if messages %}    {% for message in messages %}        <div class="alert alert-{{ message.tags }}"             data-level="{{ message.level }}"             data-level-tag="{{ message.level_tag }}"             data-extra-tags="{{ message.extra_tags }}">                        <!-- Message level -->            <strong>Level: {{ message.level }}</strong><br>                        <!-- Message tags -->            <strong>Tags: {{ message.tags }}</strong><br>                        <!-- Message text -->            {{ message.message }}                        <!-- Check message level -->            {% if message.level == DEFAULT_MESSAGE_LEVELS.ERROR %}                <p class="error-details">An error occurred</p>            {% endif %}        </div>    {% endfor %}{% endif %}

Message Storage Backends

Session Backend (Default)

# settings.pyMESSAGE_STORAGE = 'django.contrib.messages.storage.session.SessionStorage' # Stores messages in session# Pros: Simple, works with any configuration# Cons: Requires sessions

# settings.pyMESSAGE_STORAGE = 'django.contrib.messages.storage.cookie.CookieStorage' # Stores messages in cookies# Pros: No server-side storage needed# Cons: 4KB size limit, visible to user

Fallback Backend

# settings.pyMESSAGE_STORAGE = 'django.contrib.messages.storage.fallback.FallbackStorage' # Default: Tries cookie first, falls back to session# Best for most use cases

Custom Storage

# custom_storage.pyfrom django.contrib.messages.storage.base import BaseStorage class DatabaseStorage(BaseStorage):    """Store messages in database"""        def _get(self, *args, **kwargs):        # Retrieve messages from database        pass        def _store(self, messages, response, *args, **kwargs):        # Store messages in database        pass # settings.pyMESSAGE_STORAGE = 'myapp.custom_storage.DatabaseStorage'

Advanced Usage

Context Processor

# Messages available in all templates via context processor# Already included by default in settings.py: TEMPLATES = [{    'OPTIONS': {        'context_processors': [            # ...            'django.contrib.messages.context_processors.messages',        ],    },}] # Access in any template:{% if messages %}    {% for message in messages %}        {{ message }}    {% endfor %}{% endif %}

Checking for Messages

# In viewsfrom django.contrib.messages import get_messages def my_view(request):    # Get message storage    storage = get_messages(request)        # Check if has messages    if storage:        print("Has messages")        # Count messages    message_count = len(storage)        # Iterate without removing    for message in storage:        print(f"Level: {message.level}, Message: {message}")        # Messages not removed until iterated in template    return render(request, 'template.html')

Filtering Messages by Level

# In template{% if messages %}    <!-- Show only error messages -->    {% for message in messages %}        {% if message.level == DEFAULT_MESSAGE_LEVELS.ERROR %}            <div class="error">{{ message }}</div>        {% endif %}    {% endfor %}        <!-- Show success messages separately -->    {% for message in messages %}        {% if message.level == DEFAULT_MESSAGE_LEVELS.SUCCESS %}            <div class="success">{{ message }}</div>        {% endif %}    {% endfor %}{% endif %}

Messages in AJAX Requests

# views.pyfrom django.http import JsonResponsefrom django.contrib import messages def ajax_view(request):    # Process request    result = process_data()        if result['success']:        messages.success(request, 'Data processed successfully')    else:        messages.error(request, 'Failed to process data')        # Return messages as JSON    storage = messages.get_messages(request)    message_list = [        {            'level': message.level,            'message': message.message,            'tags': message.tags        }        for message in storage    ]        return JsonResponse({        'success': result['success'],        'messages': message_list    }) # JavaScriptfetch('/ajax-endpoint/')    .then(response => response.json())    .then(data => {        data.messages.forEach(msg => {            showNotification(msg.message, msg.tags);        });    });

Messages with HTML

from django.utils.safestring import mark_safe def my_view(request):    # HTML in message (be careful with user input!)    messages.success(        request,        mark_safe('Profile updated! <a href="/profile/">View profile</a>')    )        # Safe user input    username = escape(request.user.username)    messages.info(        request,        mark_safe(f'Welcome back, <strong>{username}</strong>!')    )

Practical Examples

Form Validation Messages

def create_post_view(request):    if request.method == 'POST':        form = PostForm(request.POST, request.FILES)                if form.is_valid():            post = form.save(commit=False)            post.author = request.user            post.save()                        messages.success(                request,                f'Post "{post.title}" created successfully!'            )            return redirect('post_detail', pk=post.pk)        else:            # Show error count            error_count = len(form.errors)            messages.error(                request,                f'Please correct {error_count} error(s) below.'            )                        # Show specific field errors            for field, errors in form.errors.items():                for error in errors:                    messages.error(                        request,                        f'{field}: {error}',                        extra_tags='field-error'                    )    else:        form = PostForm()        return render(request, 'create_post.html', {'form': form})

Confirmation Messages

def delete_post_view(request, pk):    post = get_object_or_404(Post, pk=pk)        # Check permission    if post.author != request.user:        messages.error(request, 'You can only delete your own posts')        return redirect('post_list')        if request.method == 'POST':        post_title = post.title        post.delete()                messages.success(            request,            f'Post "{post_title}" has been deleted.'        )        return redirect('post_list')        return render(request, 'confirm_delete.html', {'post': post})

Multi-Step Process Messages

def checkout_step1(request):    # Validate cart    if not request.session.get('cart'):        messages.warning(request, 'Your cart is empty')        return redirect('shop')        if request.method == 'POST':        # Save shipping info        request.session['shipping'] = request.POST.dict()        messages.info(request, 'Shipping information saved')        return redirect('checkout_step2')        return render(request, 'checkout_step1.html') def checkout_step2(request):    if not request.session.get('shipping'):        messages.error(request, 'Please complete shipping information first')        return redirect('checkout_step1')        if request.method == 'POST':        # Process payment        if process_payment(request):            messages.success(                request,                'Payment successful! Order confirmation sent to your email.'            )            return redirect('order_complete')        else:            messages.error(request, 'Payment failed. Please try again.')        return render(request, 'checkout_step2.html')

Background Task Messages

# Start background taskdef export_data_view(request):    # Queue export task    task_id = export_data_task.delay(request.user.id)        messages.info(        request,        'Export started. You will receive an email when complete.'    )        return redirect('dashboard') # After task completion (in task or callback)def notify_export_complete(user_id, file_url):    from django.contrib.sessions.models import Session        # This is tricky - messages are session-based    # Better to use email or database notifications    # Or use real-time notifications (WebSockets)

Bài Tập

Bài 1: Complete Message System

Task: Implement comprehensive message system:

# Requirements:# 1. Show messages for all CRUD operations#    - Create: "X created successfully"#    - Update: "X updated successfully"#    - Delete: "X deleted successfully"#    - Error: "Failed to X" # 2. Form validation messages#    - List all field errors#    - Highlight error fields # 3. Styled messages with Bootstrap#    - Success: green alert#    - Error: red alert#    - Warning: yellow alert#    - Info: blue alert # 4. Auto-dismiss after 5 seconds# 5. Manual close button# 6. Smooth fade in/out animation# 7. Toast notification position (top-right)

Bài 2: Message Filtering

Task: Create message center:

# Features:# 1. Separate sections for each level#    - Errors section (red)#    - Warnings section (yellow)#    - Success section (green)#    - Info section (blue) # 2. Show message count per level# 3. Collapsible sections# 4. Mark messages as read# 5. Clear all messages button# 6. Persist messages in database# 7. Show history of last 50 messages

Bài 3: AJAX Messages

Task: Implement AJAX message handling:

# Requirements:# 1. AJAX form submission# 2. Return messages as JSON# 3. Display messages without page reload# 4. Show success/error messages in modal# 5. Update message count in navbar# 6. Real-time message updates# 7. Handle multiple simultaneous messages # Example:# - Add to cart → Show success toast# - Like post → Show info message# - Delete comment → Show confirmation message

Bài 4: Advanced Notifications

Task: Create notification system:

# Features:# 1. Different message types:#    - System notifications#    - User notifications (mentions, replies)#    - Admin notifications # 2. Notification center dropdown#    - Unread count badge#    - Mark as read#    - Delete notification # 3. Email notifications#    - Send important messages via email#    - Configurable in user preferences # 4. WebSocket real-time notifications#    - Push notifications without refresh#    - Desktop notifications (browser API) # 5. Notification preferences#    - Enable/disable per type#    - Email vs web notification

Tài Liệu Tham Khảo

Previous: Bài 15: Sessions and Cookies | Next: Bài 17: Middleware

#flash-messages

Django Messages Framework