Add class to form field Django ModelForm

I am trying to write a Bootstrap Form with Django ModelForm. I have read the Django Documentation Django Documentation about Forms, so I have this code:

<div class="form-group">
{{ form.subject.errors }}
<label for="{{ form.subject.id_for_label }}">Email subject:</label>
{{ form.subject }}</div>

The {{form.subject}} is rendered by Django, for example in CharField field model, as input tag,

<input type="text"....> etc.

I need add "form-control" class to every input in order to get Bootstrap input appearance (without third-party packages). I found this solution Django add class to form field. Is there any way to add a class to every field by default without specifying it in every attribute of the class of Form class?

class ExampleForm(forms.Form):
   name = forms.CharField(widget=forms.TextInput(attrs={'class':'form-control'}))
   email = forms.CharField(widget=forms.TextInput(attrs={'class':'form-control'}))
   address = forms.CharField(widget=forms.TextInput(attrs={'class':'form-control'}))
   country = forms.CharField(widget=forms.TextInput(attrs={'class':'form-control'}))

and so on ..

If you can't use a third-party app and want to add a class (e.g., "form-control") to every field in a form in a DRY manner, you can do so in the form class __init__() method like so:

class ExampleForm(forms.Form):
    # Your declared form fields here
    ...

    def __init__(self, *args, **kwargs):
        super(ExampleForm, self).__init__(*args, **kwargs)
        for visible in self.visible_fields():
            visible.field.widget.attrs['class'] = 'form-control'

You might need to handle checking for existing classes in attrs too, if for some reason you'll be adding classes both declaratively and within __init__(). The above code doesn't account for that case.

Worth mentioning:

You specified that you don't want to use third-party packages. However, I'll take one second to mention that one of the simplest ways of automatically making forms render in the style of Bootstrap is to use django-crispy-forms, like this:

# settings.py
CRISPY_TEMPLATE_PACK = 'bootstrap3'

# forms.py
from crispy_forms.helper import FormHelper
class ExampleForm(forms.Form):
    # Your declared form fields here
    ...
    helper = FormHelper()

# In your template, this renders the form Bootstrap-style:
{% load crispy_forms_tags %}
{% crispy form %}

you can add CSS classes in forms.py

subject = forms.CharField(label='subject', max_length=100 , widget=forms.TextInput(attrs={'class': "form-control"}))

Since it took me more hours, than I would like to (django newbie), to figure this out, I will place my outcome here aswell.

Setting widget to each field just to add one class over and over again is against programming rule of repeating and leads to many unneccessary rows. This especially happens when working with bootstrap forms.

Here is my (working) example for adding not only bootstrap classes:

forms.py

class CompanyForm(forms.Form):
    name = forms.CharField(label='Jméno')
    shortcut = forms.CharField(label='Zkratka')
    webpage = forms.URLField(label='Webové stránky')
    logo = forms.FileField(label='Logo')

templatetags/custom_tags.py

from django import template
from django.urls import reverse

register = template.Library()

@register.filter('input_type')
def input_type(ob):
    '''
    Extract form field type
    :param ob: form field
    :return: string of form field widget type
    '''
    return ob.field.widget.__class__.__name__


@register.filter(name='add_classes')
def add_classes(value, arg):
    '''
    Add provided classes to form field
    :param value: form field
    :param arg: string of classes seperated by ' '
    :return: edited field
    '''
    css_classes = value.field.widget.attrs.get('class', '')
    # check if class is set or empty and split its content to list (or init list)
    if css_classes:
        css_classes = css_classes.split(' ')
    else:
        css_classes = []
    # prepare new classes to list
    args = arg.split(' ')
    for a in args:
        if a not in css_classes:
            css_classes.append(a)
    # join back to single string
    return value.as_widget(attrs={'class': ' '.join(css_classes)})

reusable_form_fields.html (template)

{% load custom_tags %}

{% csrf_token %}
{% for field in form %}
    <div class="form-group row">
        {% if field|input_type == 'TextInput' %}
            <div for="{{ field.label }}" class="col-sm-2 col-form-label">
                {{ field.label_tag }}
            </div>
            <div class="col-sm-10">
                {{ field|add_classes:'form-control'}}
                {% if field.help_text %}
                    <small class="form-text text-muted">{{ field.help_text }}</small>
                {% endif %}
            </div>
        {% else %}
            ...
        {% endif %}
    </div>
{% endfor %}

Crispy forms are the way to go . Tips for Bootstrap 4. Adding to @Christian Abbott's answer, For forms , bootstrap says, use form-group and form-control . This is how it worked for me .

My forms.py

class BlogPostForm(forms.ModelForm):
    class Meta:
        model = models.Post
        fields = ['title', 'text', 'tags', 'author', 'slug']
    helper = FormHelper()
    helper.form_class = 'form-group'
    helper.layout = Layout(
        Field('title', css_class='form-control mt-2 mb-3'),
        Field('text', rows="3", css_class='form-control mb-3'),
        Field('author', css_class='form-control mb-3'),
        Field('tags', css_class='form-control mb-3'),
        Field('slug', css_class='form-control'),
    )

My post_create.html

{% extends 'blog/new_blog_base.html' %}
{% load crispy_forms_tags %}
{% block content %}
<div class="container">

<form method='POST' enctype="multipart/form-data">
	{% csrf_token %}
	{{ form.media }}
	{% crispy form %}

<hr>
<input type="submit" name="Save" value="Save" class='btn btn-primary'> <a href="{% url 'home' %}" class='btn btn-danger'>Cancel</a>
</form>

</div>
{% endblock %}

Note : If you are using CK Editor RichTextField() for your model field , then that field wont be affected . If anyone knows about it , do update this .

You can also explicity mention the field that you want to apply the class to

class ProfileForm(ModelForm):

   class Meta:
       model = Profile 
        fields = ['avatar','company']  
    
    
        def __init__(self, *args, **kwargs):
           super().__init__(*args, **kwargs)
           self.fields['avatar'].widget.attrs.update({'class': 'form-control'})
           self.fields['company'].widget.attrs.update({'class':'form-control'})

I found it easier to identify the element via css and add the styling there. With django forms you get a unique id for each form field (user form prefixes if you display the form multiple times in your template).

# views.py
def my_view_function(request):
    form_a = MyForm(prefix="a")
    form_b = MyForm(prefix="b")
    context = {
        "form_a": form_a,
        "form_b": form_b
    }
    return render(request, "template/file.html", context)

style

// file.css
form input#by_id {
  width: 100%;
}

This is a answer complemeting @Christian Abbott correct answer.

If you use a lot of forms, a option for not having to override init every single time may be to create your own form class:

class MyBaseForm(forms.Form):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        for visible in self.visible_fields():
            visible.field.widget.attrs['class'] = 'form-control'

Then you can inherit from this class and it is going to automatically make the styles for you.

class ExampleForm(MyBaseForm):
    # Your declared form fields here
    ...

Same thing can be done with ModelForm by simply creating a MyBaseModelForm that inherits from ModelForm.

One way is to create base form class and manually update the field's attribute inside __init__ method.

Another is by using already existing libraries like this one: https://github.com/dyve/django-bootstrap3

There are plenty of these libraries around github. Look around.

Ok some time has passed but i had the same issues. I came to this solution:

class FormCssAttrsMixin():
    cssAttrs = {}

    def inject_css_attrs(self):
        # iterate through fields
        for field in self.fields:
            widget = self.fields[field].widget
            widgetClassName = widget.__class__.__name__

            # found widget which should be manipulated?
            if widgetClassName in self.cssAttrs.keys():
                # inject attributes
                attrs = self.cssAttrs[widgetClassName]
                for attr in attrs:
                    if attr in widget.attrs:  # attribute already existing
                        widget.attrs.update[attr] = widget[attr] + " " +    attrs[attr]  # append
                    else:  # create attribute since its not existing yet
                        widget.attrs[attr] = attrs[attr]


class MyForm(FormCssAttrsMixin, forms.Form):
    # add class attribute to all django textinputs widgets
    cssAttrs = {"TextInput": {"class": "form-control"}}

    name = forms.CharField()
    email = forms.CharField()
    address = forms.CharField()
    country = forms.CharField()

    def __init__(self, *args, **kwargs) -> None:
        super().__init__(*args, **kwargs)

        self.inject_css_attrs()

With this Mixin class you can manipulate the attributes of form widgets in a generic way. Simply add a dictionary as class variable which contains the desired attributes and values per widget. This way you can add your css classes at the same location where you define your fields. Only downside is, that you have to call the "inject_css_attrs" method somewhere but i think that is ok.

This is very practical:

class CreateSomethingForm(forms.ModelForm):

    class Meta:
        model = Something
        exclude = []

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        for field in self.fields.values():
            field.widget.attrs['class'] = 'form-control'

In this way you don't have to go field by field.

A generalized version of @christian-abbott response:

class ExampleForm(forms.Form):
    
    _HTML_CLASSES = ('form-control', 'something-else')
    
    # Your declared form fields here
    ...

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
		for visible in self.visible_fields():
			missing_classes = list(self._HTML_CLASSES)
			if 'class' in visible.field.widget.attrs:
				current_classes = visible.field.widget.attrs['class'].split(' ')
				for current_class in current_classes:
					if current_class in missing_classes:
						missing_classes.remove(current_class)
			else:
				current_classes = []
			visible.field.widget.attrs['class'] = ' '.join(current_classes + missing_classes)

I know that author asked about Bootstrap for own Form, but there is an additional way to include Bootstrap class tag in Django form for authentication, password reset etc.

If we create template with standard form:

<form action="" method="post">
   {% csrf_token %}
   {{ form }}
</form>

then in browser source code we can see all the form fields with the tags:

<form action="" method="post">
<input type="hidden" name="csrfmiddlewaretoken" value="xxx">
	<tr><th><label for="id_old_password">Old password:</label></th><td><input type="password" name="old_password" autofocus required id="id_old_password"></td></tr>
	<tr><th><label for="id_new_password1">New password:</label></th><td><input type="password" name="new_password1" required id="id_new_password1"></td></tr>
	<tr><th><label for="id_new_password2">New password confirmation:</label></th><td><input type="password" name="new_password2" required id="id_new_password2"></td></tr>
</form>

Variable {{ form }} in our template now can be replaced with this code and Bootstrap classes we needed:

<div class="fieldWrapper form-group" aria-required="true">
    <label for="id_old_password">Old password:</label><span class="required">*</span>
    <input type="password" **class="form-control"** name="old_password" autofocus required id="id_old_password">
</div>

Maybe it could be useful for redesign built-in static forms.