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Django Tutorial: Creating a Range-Slider Filter

by Farid MusaApril 12th, 2021

Too Long; Didn't Read

The tutorial can be split into four sections. In the first or prerequisite section, we will install the required packages and initiate the Django project. The next section we will create a simple Django app with a model, view, and template. The fourth and last section will describe how to create a range-slider and integrate it into our Django app created in the third section. The target filter-field isnamed. The range slider is a simple integer filter provided by django-filters.

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featured image - Django Tutorial: Creating a Range-Slider Filter

In this tutorial, we are going to create a nice crispy range slider using django-crispy-forms for an integer filter provided by django-filters. The tutorial can be split into four sections. In the first or prerequisite section, we will install the required packages and initiate the Django project. In the next section, we will create a simple app with a model, view, and template. In the third section, we will create the simple range filter using django-filters package without a slider. In the fourth and last section, we will describe how to create a range-slider and integrate it into our Django app created in the third section.

Prerequisite

First things first, let’s create a directory with the working environment:

$ mkdir myproject
$ cd myproject
$ pipenv shell

Then, install packages that are required in this tutorial using pip:

$ pip install Django
$ pip install django-crispy-forms
$ pip install django-filter

Next, create a new Django project called myproject:

$ django-admin startproject myproject
$ mv myproject src

Similarly, create a new Django app called myapp:

$ python manage.py startapp myapp

In the following sections, you are going to need to generate sample data for our model. Hence, let’s create a new Django admin super-user using the following command:

$ python manage.py createsuperuser

To enable packages in Django project, add the following lines to the

INSTALLED_APPS

/src/myproject/settings.py

INSTALLED_APPS = [
    ...
    'django.forms', # Required in the last section.
    'django_filters', # Django-filter
    'crispy_forms',
    'myapp'
]

Then, add the following line to

TEMPLATES

/src/myproject/settings.py

TEMPLATES = [
    {
        ...
        'DIRS': [BASE_DIR / 'templates'],
        ...
    },
]

Next, add the path

/src/myproject/static

STATICFILES_DIRS

/src/myproject/settings.py

to enable the CSS and JS files, which will be required in upcoming sections:

...
STATICFILES_DIRS = [ BASE_DIR / 'static']
...

Finally, add the following line of code to

/src/myproject/settings.py

to enable widget customization in our Django project.

...
FORM_RENDERER = 'django.forms.renderers.TemplatesSetting'
...

Getting Ready

In this section, we will create a model called People, a view for this model, and a template for that view.

The Model

Create a model called

People

using three fields name, surname, and age. The target filter-field is

IntegerField

named age:

class People(models.Model):
    name = models.CharField(null=True,blank=True,max_length=50)
    surname = models.CharField(null=True,blank=True,max_length=50)
    age = models.IntegerField()

Run

makemigrations

and then

migrate

to apply the change to the default SQLite database:

$ python manage.py makemigrations
$ python manage.py migrate

Then, register the model in Django admin by adding the following code to file

/src/myapp/admin.py

from django.contrib import admin
from .models import People

class PeopleAdmin(admin.ModelAdmin):
    pass

admin.site.register(People, PeopleAdmin)

NOTE: Add some items to the database from the Django admin page at http://127.0.0.1:8000/admin/.

The View

Now let’s create a simple view that will print all instances of

People

model in

/src/myapp/views.py

from django.shortcuts import render
from .models import People

def index(request):
    all_people = People.objects.all()
    return render(request, 'index.html', {'all_people':all_people})

URLs

Create a URL path by adding the following line to the file

/src/myproject/urls.py

...
from myapp.views import index

urlpatterns = [
    ...
    path('', index),
]

The Template

In order to create the simplest template to render all

People

instances, create a file

/src/templates/index.html

with the following content:

<table border='1' style="width:100%; text-align:center">
  <thead>
    <tr>
      <th> Name </th>
      <th> Surname </th>
      <th> Age </th>
    </tr>
  </thead>

  <tbody>
    {% for person in all_people %}
    <tr>
      <td> {{ person.name }} </td>
      <td> {{ person.surname }} </td>
      <td> {{ person.age }} </td>
    </tr>
    {% endfor %}
  </tbody>
</table>

Recap

In this section, we created a simple view and template to print database records for

People

the model. Executing

$ python manage.py runserver

should make available the following screen:

Naive Range Filter

In order to ensure coherence let’s first create a simple(or naive)

RangeFilter

provide by django-filters package.

The Filter

Create a new file

/src/myapp/filters.py

and insert the following code:

import django_filters
from .models import People

class PeopleFilter(django_filters.FilterSet):
  age = django_filters.AllValuesFilter()

  class Meta:
      model = People
      fields = ['age']

This will create a simple range-filter with minimum and maximum value requirements for

age

field of

People

model.

The View

Now that filtering logic is ready, let’s add the filtering feature to the main view in

/src/myapp/views.py

from django.shortcuts import render
from .filters import PeopleFilter

def index(request):
    people_filter = RangeFilter(request.GET)
    return render(request, 'index.html', {'people_filter':people_filter})

In the above code,

RangeFilter

instantiation takes

request.GET

as a single parameter since our form is set to GET mode.

The Template

With our filter ready, we can add filter controls in the front. Once again change the primary template file

/src/template/index.html

to look like this:

<form method="get">
    {{ people_filter.form.as_p }}
    <input type="submit" />
</form>

<table border='1' style="width:100%; text-align:center">
  <thead>
    <tr>
      <th> Name </th>
      <th> Surname </th>
      <th> Age </th>
    </tr>
  </thead>

  <tbody>
    {% for person in people_filter.qs %}
    <tr>
      <td> {{ person.name }} </td>
      <td> {{ person.surname }} </td>
      <td> {{ person.age }} </td>
    </tr>
    {% endfor %}
  </tbody>
</table>

Notice that we now have an additional filtering form provided by django-filters. In addition, observe that for statement loops over

people_filter.qs

instead of

all_people

. The

.qs

stands for query set, which is self-explanatory.

Recap

In this section, we created the simplest or naive filter. The final result should look like this:

Crispy Range-Slider

To create a working crispy range-slider we need the following:

Front-end Backbone: Actual range-slider with HTML, CSS and JavaScript.
Django Widget: Custom Django widget for the actual range-slider backbone.
Crispy Form: Crispy form with a layout template for the custom widget.
Range Filter: Custom filter from django-filters package that utilizes the range-slider widget with the Crispy form.

Each point will be described in details so let’s move step-by-step:

The Front End

The first and obvious step is to create an actual slider. Since range-slider is fancy filtering “thing” and not a real HTML form element, let’s use a popular trick to make such a fancy “thing” act like an HTML form element. Particularly, we use jQuery’s range slider feature to make our range-slider work. Here is a sample HTML blueprint for our slider:

<div id="my-numeric-slider"
     class="form-group numeric-slider"
     data-range_min="[Min. Possible Value]"
     data-range_max="[Max. Possible Value]"
     data-cur_min="[Current Min. Value]"
     data-cur_max="[Current Max. Value]">
<div class="numeric-slider-range ui-slider ui-slider-horizontal ui-slider-range"></div>
<span class="numeric-slider-range_text" id='my-numeric-slider_text'>[Lower Value] - [Upper Value]</span>
<input type='hidden' id='my-numeric-slider_min' name='slider-min'/>
<input type='hidden' id='my-numeric-slider_max' name='slider-max'/>
</div>

The above HTML markup is comprised of outer Div element where the first two data- attributes represent possible minimum and maximum values of the range filter, last two data- attributes represent current lower and upper values of the range filter that were established when the page is loaded. Likewise, the first inner elements Div with the class

numeric-slider-range

is the main element transformed to the range slider by jQuery when the page is loaded. The last two hidden Input form-elements represent the primary means by which the data is passed from the client to the server-side when the form is submitted. Additionally, the above HTML markup requires a JS script to make the slider work and a CSS markup to render the elements properly. Both can be found in GitHub repo. Finally, apply the last template code bellow to the file

/src/templates/index.html

{% load static %}
{% load crispy_forms_tags %}

<head>
  <link rel="stylesheet" href="{% static 'custom_slider.css' %}"> # CSS of our range-slider.
  <link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">

  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
  <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>

<body>
  {% crispy people_filter.form %}

  <table border='1' style="width:100%; text-align:center">
    <thead>
      <tr>
        <th> Name </th>
        <th> Surname </th>
        <th> Age </th>
      </tr>
    </thead>

    <tbody>
      {% for person in people_filter.qs %}
      <tr>
        <td> {{ person.name }} </td>
        <td> {{ person.surname }} </td>
        <td> {{ person.age }} </td>
      </tr>
      {% endfor %}
    </tbody>
  </table>

  <script src="{% static 'custom_slider.js' %}"></script> # JS of our range-slider.
</body>

Notice that in the HTML above we load the

crispy_forms_tags

and use

{% crispy people_filter.form %}

instead of

.as_p

. Doing so we let django-crispy-forms package handle our form rendering.

NOTE: The django-crispy-forms package provides two ways to render crispy forms. Common way is to use

|crispy

filter to render the form but it expects to be wrapped in <form>...</form>
HTML tag. In our tutorial, we use {% crispy %}
tag because we will generate our form using the FormHelper
.

The Django Widget

Django uses widgets to render form-fields and present them as final HTML markup. Therefore, to let Django handle the rendering of our front-end backbone, we need a working widget. In Django, a widget consists of two parts:

a widget-template that represents the final HTML
a class that inherits Django’s
```
Widget
```
class with
```
render()
```
method.

Widget Class

The django-filters package provides working

RangeFilter

with a predefined

RangeWidget

that we seamlessly/automagically used in the previous section. This widget uses two text-fields associated with two text-input HTML form-elements. Notice that it is similar to hidden input-elements required in our case. To make our widget work we will simply rewrite the default

RangeWidget

provided by django-filter to be compatible with our range-slider. For simplicity let's call it the

CustomRangeWidget

from django.forms.widgets import HiddenInput
from django_filters.widgets import RangeWidget

class CustomRangeWidget(RangeWidget):
    template_name = 'forms/widgets/range-slider.html'

    def __init__(self, attrs=None):
        widgets = (HiddenInput(), HiddenInput())
        super(RangeWidget, self).__init__(widgets, attrs)

    def get_context(self, name, value, attrs):
        ctx = super().get_context(name, value, attrs)
        cur_min, cur_max = value
        if cur_min is None:
            cur_min = ctx['widget']['attrs']['data-range_min']
        if cur_max is None:
            cur_max = ctx['widget']['attrs']['data-range_max']
        ctx['widget']['attrs'].update({'data-cur_min':cur_min,
                                        'data-cur_max':cur_max})
        base_id = ctx['widget']['attrs']['id']
        for swx, subwidget in enumerate(ctx['widget']['subwidgets']):
            subwidget['attrs']['id'] = base_id + "_" + self.suffixes[swx]
        ctx['widget']['value_text'] = "{} - {}".format(cur_min,cur_max)
        return ctx

Widget Template

The widget also requires an associated template. Let’s create a file in

/src/templates/forms/widgets/range-slider.html

and insert the following content.

<div class="form-group numeric-slider" {% include "django/forms/widgets/attrs.html" %}>
  <div class="numeric-slider-range ui-slider ui-slider-horizontal ui-slider-range"></div>
  <span class="numeric-slider-range_text" id='{{ widget.attrs.id }}_text'>
    {{ widget.value_text }}
  </span>
  {% for widget in widget.subwidgets %}
    {% include widget.template_name %}
  {% endfor %}
</div>

In the above widget-template, we use

{% include "django/forms/widgets/attrs.html" %}

to let Django handle the widget attributes. It does so by parsing the dictionary

ctx['widget']['attrs']

from the previous part. Likewise, the

for

loop adds widget’s

HiddenInput

elements.

The Crispy Form

At last, we have our actual widget ready and now we can create a crispy-form with a special template for our slider. This crispy layout template basically helps our widget to fit the Bootstrap markup logic. In other words, it makes it crispy.

Crispy Template

Create a new file

/src/templates/forms/fields/range-slider.html

. Then add the following template code:

{% load crispy_forms_field %}

<div class="form-group{% if 'form-horizontal' in form_class %} row{% endif %}">
  <label for="{{ field.id_for_label }}" class="{% if 'form-horizontal' in form_class %}col-form-label {% endif %}{{ label_class }}{% if field.field.required %} requiredField{% endif %}">
    {{ field.label|safe }}
    {% if field.field.required %}
      <span class="asteriskField">*</span>
    {% endif %}
  </label>
  {% crispy_field field  %}
</div>

NOTE: the above code is based on django-crispy-forms’s bootstrap4 templates and was not tested in bootstrap3 or other crispy template-engine.

Crispy Form Helper

Once the crispy template is ready we need a form where the template will be utilized. Create a file

/src/myapp/forms.py

and add the following code:

from crispy_forms.helper import FormHelper
from crispy_forms.bootstrap import StrictButton
from crispy_forms.layout import Field, Layout
from django import forms
from django_filters.fields import RangeField

class PeopleFilterFormHelper(forms.Form):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.helper = FormHelper(self)
        self.helper.form_method = 'get'
        layout_fields = []
        for field_name, field in self.fields.items():
            if isinstance(field, RangeField):
                layout_field = Field(field_name, template="forms/fields/range-slider.html")
            else:
                layout_field = Field(field_name)
            layout_fields.append(layout_field)
        layout_fields.append(StrictButton("Submit", name='submit', type='submit', css_class='btn btn-fill-out btn-block mt-1'))
        self.helper.layout = Layout(*layout_fields)

In the code above the class

PeopleFilterFormHelper

is nothing different than a simple Django form with a fancy name. However, instead of a common way of constructing Django form we use the Crispy approach with its

FormHelper

NOTE: the

FormHelper

simply helps you to create a fancy form, which would most certainly be possible to create with the same Django means but with more effort. Our form is rather basic for the sake of clarity of our tutorial, so it is not obvious.

Range Filter

At last, we have everything ready except the actual filtering logic.

Custom Range Filter

Insert following final filter code to the file

/src/myapp/filters.py

from django_filters import FilterSet
from django_filters.filters import RangeFilter
from .models import People
from .forms import PeopleFilterFormHelper
from .widgets import CustomRangeWidget

class AllRangeFilter(RangeFilter):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        values = [p.age for p in People.objects.all()]
        min_value = min(values)
        max_value = max(values)
        self.extra['widget'] = CustomRangeWidget(attrs={'data-range_min':min_value,'data-range_max':max_value})

class PeopleFilter(FilterSet):
  age = AllRangeFilter()

  class Meta:
      model = People
      fields = ['age']
      form = PeopleFilterFormHelper

In the code above,

PeopleFilter

represents the set of filters for the model

People

. Notice the line

form = PeopleFilterFormHelper

, which overrides the default form builder of django-filters to our custom

PeopleFilterFormHelper

. The actual filter is the

AllRangeFilter

class, which is a customized version of the original django-filters package's

RangeFilter

. We override its

__init__

method and initiate our custom widget

CustomRangeWidget

with initial minimum and maximum values of all possible age values from

People

model's

age

field.

NOTE: I totally agree that list comprehension is far not the best way to get the min. and max. values but this is a tutorial and its for only for educational purpose.

Recap

At last, we created our range filter with a fancy slider that should look like this:

Summary

In this tutorial, you learned how to create a fancy jQuery range slider with the custom widget for the custom range filter provided by django-filters package. Moreover, you learned how to use render the custom widget using django-crispy-forms the package. The source code for this tutorial can be found on my GitHub repo. I hope this tutorial was helpful to the reader and eased his suffering while learning these amazing Django packages.

Previously published at https://www.mmtechslv.com/tutorials/django-crispy-range-slider/