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Django Forms: Creating and Handling HTML Forms

drwxr-xr-x2026-01-225 min0 views

Django forms handle HTML form creation, rendering, validation, and data processing providing secure form handling with CSRF protection and automatic sanitization. Forms abstract form field rendering and validation enabling reusable form logic across views and templates. Understanding Django forms is essential for accepting user input including contact forms, search forms, user registration, and data entry applications. Django provides Form class for general forms and ModelForm for forms based on models automatically generating form fields from model definitions. Mastering Django forms supports building interactive web applications with proper validation, error handling, and user feedback from simple contact forms to complex multi-step wizards and file upload interfaces ensuring data integrity and user experience quality.

Form Basics

Django Form class defines form fields with validators and widgets controlling rendering and validation. Forms handle GET rendering and POST processing through is_valid() method. Understanding form basics enables creating secure validated forms with minimal code.

pythonform_basics.py

# Form Basics
from django import forms

# Basic form
class ContactForm(forms.Form):
    name = forms.CharField(max_length=100)
    email = forms.EmailField()
    subject = forms.CharField(max_length=200)
    message = forms.CharField(widget=forms.Textarea)

# View handling form
from django.shortcuts import render, redirect

def contact_view(request):
    if request.method == 'POST':
        form = ContactForm(request.POST)
        if form.is_valid():
            # Access cleaned data
            name = form.cleaned_data['name']
            email = form.cleaned_data['email']
            subject = form.cleaned_data['subject']
            message = form.cleaned_data['message']
            
            # Process form (send email, save to DB, etc.)
            send_email(subject, message, email)
            
            return redirect('success')
    else:
        form = ContactForm()
    
    return render(request, 'contact.html', {'form': form})

# Template rendering
# <form method="post">
#     {% csrf_token %}
#     {{ form.as_p }}
#     <button type="submit">Submit</button>
# </form>

# Form field types
class UserForm(forms.Form):
    # Text inputs
    username = forms.CharField(max_length=30)
    password = forms.CharField(widget=forms.PasswordInput)
    
    # Choices
    country = forms.ChoiceField(choices=[
        ('us', 'United States'),
        ('uk', 'United Kingdom'),
        ('ca', 'Canada'),
    ])
    
    # Multiple choice
    interests = forms.MultipleChoiceField(choices=[
        ('sports', 'Sports'),
        ('music', 'Music'),
        ('reading', 'Reading'),
    ])
    
    # Boolean
    agree_terms = forms.BooleanField()
    
    # Numeric
    age = forms.IntegerField(min_value=18, max_value=100)
    rating = forms.DecimalField(max_digits=3, decimal_places=1)
    
    # Date/Time
    birth_date = forms.DateField()
    appointment_time = forms.DateTimeField()
    
    # File upload
    profile_picture = forms.ImageField()
    document = forms.FileField()
    
    # URL and Email
    website = forms.URLField()
    email = forms.EmailField()

# Initial values
form = ContactForm(initial={
    'name': 'John Doe',
    'email': '[email protected]'
})

# Required fields
class MyForm(forms.Form):
    required_field = forms.CharField()
    optional_field = forms.CharField(required=False)

Form Validation

Form validation ensures data integrity through field validators and clean methods. Field-level validation uses clean_fieldname methods while form-level validation uses clean method for cross-field validation. Understanding validation enables robust data processing with comprehensive error handling.

pythonvalidation.py

# Form Validation
from django import forms
from django.core.exceptions import ValidationError

class RegistrationForm(forms.Form):
    username = forms.CharField(max_length=30)
    email = forms.EmailField()
    password = forms.CharField(widget=forms.PasswordInput)
    confirm_password = forms.CharField(widget=forms.PasswordInput)
    age = forms.IntegerField()
    
    # Field-level validation
    def clean_username(self):
        username = self.cleaned_data['username']
        
        # Check if username exists
        if User.objects.filter(username=username).exists():
            raise ValidationError('Username already taken')
        
        # Custom validation
        if len(username) < 3:
            raise ValidationError('Username must be at least 3 characters')
        
        if not username.isalnum():
            raise ValidationError('Username must be alphanumeric')
        
        return username
    
    def clean_email(self):
        email = self.cleaned_data['email']
        
        if User.objects.filter(email=email).exists():
            raise ValidationError('Email already registered')
        
        # Domain validation
        if not email.endswith('@example.com'):
            raise ValidationError('Must use company email')
        
        return email
    
    def clean_age(self):
        age = self.cleaned_data['age']
        
        if age < 18:
            raise ValidationError('Must be 18 or older')
        
        return age
    
    # Form-level validation (cross-field)
    def clean(self):
        cleaned_data = super().clean()
        password = cleaned_data.get('password')
        confirm_password = cleaned_data.get('confirm_password')
        
        if password and confirm_password:
            if password != confirm_password:
                raise ValidationError('Passwords do not match')
        
        return cleaned_data

# Custom validators
from django.core.validators import RegexValidator

def validate_no_spaces(value):
    if ' ' in value:
        raise ValidationError('Value cannot contain spaces')

class MyForm(forms.Form):
    username = forms.CharField(
        validators=[
            validate_no_spaces,
            RegexValidator(r'^[a-zA-Z0-9_]+$', 'Only alphanumeric and underscores')
        ]
    )

# Multiple validation errors
def clean_username(self):
    username = self.cleaned_data['username']
    errors = []
    
    if len(username) < 3:
        errors.append('Too short')
    
    if not username[0].isalpha():
        errors.append('Must start with letter')
    
    if errors:
        raise ValidationError(errors)
    
    return username

Form Rendering

Form rendering controls HTML output through templates and widgets. Django provides helper methods like as_p, as_table, and as_ul for quick rendering or manual field rendering for custom layouts. Understanding rendering enables creating forms matching application design requirements.

pythonrendering.py

# Form Rendering

# Template - Automatic rendering
# As paragraphs
# <form method="post">
#     {% csrf_token %}
#     {{ form.as_p }}
#     <button type="submit">Submit</button>
# </form>

# As table
# <form method="post">
#     {% csrf_token %}
#     <table>
#         {{ form.as_table }}
#     </table>
#     <button type="submit">Submit</button>
# </form>

# Manual field rendering
# <form method="post">
#     {% csrf_token %}
#     
#     <div class="field">
#         {{ form.username.label_tag }}
#         {{ form.username }}
#         {% if form.username.errors %}
#             <span class="error">{{ form.username.errors }}</span>
#         {% endif %}
#     </div>
#     
#     <div class="field">
#         {{ form.email.label_tag }}
#         {{ form.email }}
#         {% if form.email.errors %}
#             <span class="error">{{ form.email.errors }}</span>
#         {% endif %}
#     </div>
#     
#     <button type="submit">Submit</button>
# </form>

# Display all errors
# {% if form.errors %}
#     <div class="errors">
#         <ul>
#         {% for field in form %}
#             {% for error in field.errors %}
#                 <li>{{ field.label }}: {{ error }}</li>
#             {% endfor %}
#         {% endfor %}
#         {% for error in form.non_field_errors %}
#             <li>{{ error }}</li>
#         {% endfor %}
#         </ul>
#     </div>
# {% endif %}

# Custom widgets
from django import forms

class StyledForm(forms.Form):
    name = forms.CharField(
        widget=forms.TextInput(attrs={
            'class': 'form-control',
            'placeholder': 'Enter your name'
        })
    )
    
    message = forms.CharField(
        widget=forms.Textarea(attrs={
            'rows': 5,
            'cols': 40,
            'class': 'form-control'
        })
    )
    
    country = forms.ChoiceField(
        choices=[('us', 'USA'), ('uk', 'UK')],
        widget=forms.RadioSelect
    )

# Widget in Meta
class UserForm(forms.ModelForm):
    class Meta:
        model = User
        fields = ['username', 'email', 'bio']
        widgets = {
            'bio': forms.Textarea(attrs={'rows': 4}),
            'email': forms.EmailInput(attrs={'class': 'form-control'})
        }

ModelForms

ModelForm automatically generates form fields from model definitions reducing code duplication and ensuring consistency between models and forms. ModelForm saves directly to database with form.save() method. Understanding ModelForm enables rapid form development for CRUD operations.

pythonmodelforms.py

# ModelForms
from django import forms
from .models import Post

# Basic ModelForm
class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        fields = ['title', 'content', 'status']
        # Or exclude fields
        # exclude = ['created_at', 'updated_at']
        # Or all fields
        # fields = '__all__'

# View using ModelForm
def create_post(request):
    if request.method == 'POST':
        form = PostForm(request.POST)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.save()
            return redirect('post_detail', pk=post.pk)
    else:
        form = PostForm()
    
    return render(request, 'post_form.html', {'form': form})

# Update view
def update_post(request, pk):
    post = get_object_or_404(Post, pk=pk)
    
    if request.method == 'POST':
        form = PostForm(request.POST, instance=post)
        if form.is_valid():
            form.save()
            return redirect('post_detail', pk=pk)
    else:
        form = PostForm(instance=post)
    
    return render(request, 'post_form.html', {'form': form})

# Custom labels and help text
class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        fields = ['title', 'content', 'status']
        labels = {
            'title': 'Post Title',
            'content': 'Post Content',
        }
        help_texts = {
            'title': 'Enter a catchy title',
        }
        error_messages = {
            'title': {
                'required': 'Please provide a title',
            }
        }

# Override fields
class PostForm(forms.ModelForm):
    # Override field
    title = forms.CharField(
        max_length=200,
        widget=forms.TextInput(attrs={'class': 'form-control'})
    )
    
    class Meta:
        model = Post
        fields = ['title', 'content', 'status']
    
    def clean_title(self):
        title = self.cleaned_data['title']
        if 'spam' in title.lower():
            raise forms.ValidationError('Invalid title')
        return title

# Many-to-many handling
form = PostForm(request.POST)
if form.is_valid():
    post = form.save(commit=False)
    post.author = request.user
    post.save()
    form.save_m2m()  # Save many-to-many relationships

Form Best Practices

Effective form usage follows patterns ensuring security and usability. Always include CSRF token in POST forms. Use ModelForm when forms correspond to models. Validate data thoroughly with clean methods. Provide clear error messages. Use appropriate widgets for field types. Handle file uploads securely. Implement form success messages. Test form validation thoroughly. Keep forms focused avoiding too many fields. Use crispy-forms or similar for consistent styling. These practices ensure secure, user-friendly forms supporting reliable data collection and processing.