Showing posts with label Widget. Show all posts
Showing posts with label Widget. Show all posts

2019-10-08

Working with Dates and Times in the Forms

HTML5 comes with a bunch of new types for the input fields that are rendered as rich native widgets. Browsers even restrict invalid values and validate the input immediately. Let's explore how we could make use of them in Django forms.

We will be using an Exhibition model with models.DateField, models.TimeField, and models.DateTimeField:

# exhibitions/models.py
from django.db import models
from django.utils.translation import gettext_lazy as _

class Exhibition(models.Model):
    title = models.CharField(_("Title"), max_length=200)
    start = models.DateField(_("Start"))
    end = models.DateField(_("End"), blank=True, null=True)
    opening = models.TimeField(_("Opening every day"))
    closing = models.TimeField(_("Closing every day"))
    vernissage = models.DateTimeField(_("Vernissage"), blank=True, null=True)
    finissage = models.DateTimeField(_("Finissage"), blank=True, null=True)

    class Meta:
        verbose_name = _("Exhibition")
        verbose_name_plural = _("Exhibitions")

    def __str__(self):
        return self.title

Here is a quick model form for the Exhibition model:

# exhibitions/forms.py
from django import forms
from .models import Exhibition

class ExhibitionForm(forms.ModelForm):
    class Meta:
        model = Exhibition
        fields = "__all__"

If we now open a Django shell and create an instance of the model form with some initial values, then print the form as HTML to the console, we will notice, that all date and time fields are rendered as <input type="text" /> and the values for the dates are in a local format, not the ISO standard YYYY-MM-DD:

(venv)$ python manage.py shell
>>> from exhibitions.forms import ExhibitionForm
>>> from datetime import datetime, date, time
>>> form = ExhibitionForm(initial={
...     "start": date(2020, 1, 1),
...     "end": date(2020, 3, 31),
...     "opening": time(11, 0),
...     "closing": time(20, 0),
...     "vernissage": datetime(2019, 12, 27, 19, 0),
...     "finissage": datetime(2020, 4, 1, 19, 0),
>>> })
>>> print(form.as_p())
<p><label for="id_title">Title:</label> <input type="text" name="title" maxlength="200" required id="id_title"></p>
<p><label for="id_start">Start:</label> <input type="text" name="start" value="01.01.2020" required id="id_start"></p>
<p><label for="id_end">End:</label> <input type="text" name="end" value="31.03.2020" id="id_end"></p>
<p><label for="id_opening">Opening every day:</label> <input type="text" name="opening" value="11:00:00" required id="id_opening"></p>
<p><label for="id_closing">Closing every day:</label> <input type="text" name="closing" value="20:00:00" required id="id_closing"></p>
<p><label for="id_vernissage">Vernissage:</label> <input type="text" name="vernissage" value="27.12.2019 19:00:00" id="id_vernissage"></p>
<p><label for="id_finissage">Finissage:</label> <input type="text" name="finissage" value="01.04.2020 19:00:00" id="id_finissage"></p>

Let's modify the model form and customize the date and time inputs. We will extend and use forms.DateInput, forms.TimeInput, and forms.DateTimeInput widgets. We want to show date inputs as <input type="date" />, time inputs as <input type="time" />, and date-time inputs as <input type="datetime-local" />. In addition, the format for the dates should be based on ISO standard.

# exhibitions/forms.py
from django import forms
from .models import Exhibition


class DateInput(forms.DateInput):
    input_type = "date"

    def __init__(self, **kwargs):
        kwargs["format"] = "%Y-%m-%d"
        super().__init__(**kwargs)


class TimeInput(forms.TimeInput):
    input_type = "time"


class DateTimeInput(forms.DateTimeInput):
    input_type = "datetime-local"

    def __init__(self, **kwargs):
        kwargs["format"] = "%Y-%m-%dT%H:%M"
        super().__init__(**kwargs)


class ExhibitionForm(forms.ModelForm):
    class Meta:
        model = Exhibition
        fields = "__all__"

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields["start"].widget = DateInput()
        self.fields["end"].widget = DateInput()
        self.fields["opening"].widget = TimeInput()
        self.fields["closing"].widget = TimeInput()
        self.fields["vernissage"].widget = DateTimeInput()
        self.fields["vernissage"].input_formats = ["%Y-%m-%dT%H:%M", "%Y-%m-%d %H:%M"]
        self.fields["finissage"].widget = DateTimeInput()
        self.fields["finissage"].input_formats = ["%Y-%m-%dT%H:%M", "%Y-%m-%d %H:%M"]

Let's see now in the Django shell if that worked as expected:

(venv)$ python manage.py shell
>>> from exhibitions.forms import ExhibitionForm
>>> from datetime import datetime, date, time
>>> form = ExhibitionForm(initial={
...     "start": date(2020, 1, 1),
...     "end": date(2020, 3, 31),
...     "opening": time(11, 0),
...     "closing": time(20, 0),
...     "vernissage": datetime(2019, 12, 27, 19, 0),
...     "finissage": datetime(2020, 4, 1, 19, 0),
>>> })
>>> print(form.as_p())
<p><label for="id_title">Title:</label> <input type="text" name="title" maxlength="200" required id="id_title"></p>
<p><label for="id_start">Start:</label> <input type="date" name="start" value="2020-01-01" required id="id_start"></p>
<p><label for="id_end">End:</label> <input type="date" name="end" value="2020-03-31" id="id_end"></p>
<p><label for="id_opening">Opening every day:</label> <input type="time" name="opening" value="11:00:00" required id="id_opening"></p>
<p><label for="id_closing">Closing every day:</label> <input type="time" name="closing" value="20:00:00" required id="id_closing"></p>
<p><label for="id_vernissage">Vernissage:</label> <input type="datetime-local" name="vernissage" value="2019-12-27T19:00" id="id_vernissage"></p>
<p><label for="id_finissage">Finissage:</label> <input type="datetime-local" name="finissage" value="2020-04-01T19:00" id="id_finissage"></p>

The same way you can also create widgets for other HTML5 input types: color, email, month, number, range, tel, url, week, and alike.

Happy coding!


Cover photo by Eric Rothermel.

2019-04-27

Improving Page Speed with Incremental Loading

Improving Page Speed with Incremental Loading

Summary: you can use django-include-by-ajax to improve the performance and usability of your website by forcing some parts of the Django website page to be loaded and shown before other parts of the page.


Web browsers load and render traditional HTML pages from top to down, from left to right and as a developer you have little control over what will be shown first, second, and last. However, sometimes you need a different loading sequence to improve user experience and usability. Let's examine a couple of cases when it is advantageous to have primary content showing up immediately and secondary content loading in a moment.

Case 1. Above the Fold vs. Below the Fold

People want speed. 47% of visitors expect the website to be loaded in less than 2 seconds. If the website takes more than 3 seconds to show up, it's a big chance, that you will lose 40% of visitors. If you sell something on your website, every one-second delay causes 7% fewer visitors becoming buyers.

One technique to improve the perception of the speed of the website is to display the visible part of the screen as soon as possible, and then load the rest of the website in another go. Usually, the website pages are long vertically scrollable areas. The part of it that fits in the screen is called "above the fold" and the part underneath is called "below the fold".

Primary content above the fold and secondary content below the fold

It is recommended to load the part above the fold in 6 requests, including all your HTML, CSS, JavaScript, images and fonts. It's only 6 requests for a reason - that's the maximal number of requests that most browsers keep to the same HTTP/1.1 server at the same time. With HTTP/2 there is no such limitation.

You can only achieve this minimal load if you bundle and minimize your CSS and JavaScript to single files, and use only a couple of images and fonts. Going one step further you can split your CSS and JavaScript into parts that are used above the fold, and the ones that are used below the fold.

Case 2. Main Content vs. Navigation

For the users to have best user experience and smooth loading, you could display the content of articles or blog post first, and then load and display the website navigation in the header, sidebars, or footer.

Content is primary and the navigation is secondary

If the visitor navigated to a specific page of your website, they most likely want to see the content of that page rather than navigate out to other pages.

If you have extensive nested navigation, you can also save some milliseconds of its loading at the first request, by skipping it there, but loading it by Ajax at the next go.

Additionally, if visitor disables JavaScript in their browser, they will still be able to read the content.

Case 3. Own Content vs. Third-party Content

Wouldn't you agree, websites that show ads before their own content are pretty annoying? One way to improve the user experience is to show the main content at first and show the ads or third-party widgets after several seconds.

Own content is primary and third-party widgets are secondary

The primary content will be correctly indexed by search engines, whereas the included widgets might be skipped, depending on implementation, which we'll examine next.

Solution 1. Iframes

One way to load the delayed secondary content is to use iframes.

Pros:

  • Works without JavaScript.

Cons:

  • For each iframed section, you need a separate HTML with custom CSS.
  • You have to predefine and hardcode all heights of each secondary section, so it wouldn't work well with increased or decreased font size or different amounts of content.
  • You cannot have interactive elements like tooltips that would go outside the boundaries of the iframe.

Solution 2. API Calls by Ajax

The page would load with empty placeholders for the secondary content and then some JavaScript function would load content for the missing sections in HTML, JSON, or XML format by Ajax, parse them, and include into the placeholders. This approach has been used by Facebook.

Pros:

  • You can use the same global CSS for everything.
  • The amount of content is flexible, so the designs would look good with different variations.

Cons:

  • For each secondary section, you need to define a separate API endpoint.
  • There are many extra requests (unless you use GraphQL for that).

Solution 3. A Second Request to the Same Page with Specific Query Parameters

The page loads with empty placeholders for the secondary content. A JavaScript function uses Ajax to load the HTML of the same page this time containing all rendered primary and secondary content. Then another JavaScript function goes through all placeholders and fills the content from the second load.

Pros:

  • You can use the same global CSS for everything.
  • The amount of content is flexible, so the designs could look good with different variations.
  • Each page uses a single data endpoint.
  • Only one extra request is necessary for the full HTML.

Cons:

  • If there is a lot of primary content and not so much of secondary content, it might take too long to load and parse the secondary content.

Implementation for a Django Website using django-include-by-ajax

You can implement the third solution in a Django website using my open-source Django app django-include-by-ajax. It is meant to be understandable and simple to use for frontend Django developers, who don't touch Python code but need to work on the layouts and styling.

The idea is that instead of including different sections of a template with the {% include template_name %} template tag, you do the same using {% include_by_ajax template_name %} template tag. This template tag renders as an empty placeholder unless you access the page from a search crawler or if you access the page with a specific query parameter. Otherwise, it works more-or-less the same as the {% include %} template tag.

By adding jQuery and one jQuery-based JavaScript file to your page template, you enable the magic that does all the loading and parsing. Since version 1.0, CSS and JavaScript files can also be included in those delayed sections.

You can see django-include-by-ajax in action at the start page of my personal project 1st things 1st. There I use the above-the-fold case with the visible content coming to the screen almost immediately and the offscreen content loading in several more seconds.

Installation

It should be trivial to convert any standard heavy website page to a page loading the secondary content dynamically. There are mainly these steps to follow:

  1. Install the app with your Python package manager:

    (venv)$ pip install django-include-by-ajax==1.0.0
  2. Put the app into the INSTALLED_APPS in your Django project settings:

    # settings.py
    INSTALLED_APPS = [
        # ...
        # Third-party apps
        'include_by_ajax',
        # ...
    ]
  3. Put these in your base.html:

    {% load staticfiles %}
    <script src="https://code.jquery.com/jquery-3.4.0.min.js" crossorigin="anonymous"></script>
    <script src="{% static 'include_by_ajax/js/include_by_ajax.min.js' %}" defer></script>

    It should also work with older or newer jQuery versions.

  4. Use the new template tag in any template where you need it:

    {% load include_by_ajax_tags %}
    {% include_by_ajax "blog/includes/latest_blog_posts.html" %}

    You can even define the content for the placeholder that will be shown while the main content is loading:

    {% load include_by_ajax_tags %}
    {% include_by_ajax "blog/includes/latest_blog_posts.html" placeholder_template_name="utils/loading.html" %}
  5. If you need some JavaScript action to be called after all content is loaded, you can use the custom include_by_ajax_all_loaded event on the document like this:

    $(document).on('include_by_ajax_all_loaded', function() {
        console.log('Now all placeholders are loaded and replaced with content. Hurray!');
    });

I would be glad if you tried it on some of your projects and see how it improved user experience and loading times. If you use it in production, please mention it in the comments of this blog post.

More Information

The app on Github: A Django App Providing the {% include_by_ajax %} Template Tag

The practical usage example: Strategic planner - Prioritizer - 1st things 1st.

An article on performance and usability: 5 Reasons Visitors Leave Your Website


Cover photo by Thomas Tucker.

Thanks to Adam Johnson for reviewing this post.

2016-02-06

Fresh Book for Django Developers

This week the post office delivered a package that made me very satisfied. It was a box with three paper versions of my "Web Development with Django Cookbook - Second Edition". The book was published at the end of January after months of hard, but fulfilling work in the late evenings and at weekends.

The first Django Cookbook was dealing with Django 1.6. Unfortunately, the support for that version is over. So it made sense to write an update for a newer Django version. The second edition was adapted for Django 1.8 which has a long-term support until April 2018 or later. This edition introduces new features added to Django 1.7 and Django 1.8, such as database migrations, QuerySet expressions, or System Check Framework. Most concepts in this new book should also be working with Django 1.9.

My top 5 favourite new recipes are these:

  • Configuring settings for development, testing, staging, and production environments
  • Using database query expressions
  • Implementing a multilingual search with Haystack
  • Testing pages with Selenium
  • Releasing a reusable Django app

The book is worth reading for any Django developer, but will be best understood by those who already know the basics of web development with Django. You can learn more about the book and buy it at the Packt website or Amazon.

I thank the Packt Publishing very much for long cooperation in the development of this book. I am especially thankful to acquisition editor Nadeem N. Bagban, content development editors Arwa Manasawala and Sumeet Sawant, and technical editor Bharat Patil. Also I am grateful for insightful feedback from the reviewer Jake Kronika.

What 5 recipes do you find the most useful?

2013-09-22

How to Create a File Upload Widget

Ajaxified file uploads are becoming de facto standard on the web. People want to see what they chose right after selecting a file instead of during submit of the form. Also if a form has validation errors, nobody wants to select the files again; the selection made should be still available in the form. Therefore, we need a solution that works by Ajax.

Luckily there is a Django app that can help. It's called django-ajax-uploader. Ajax uploader allows to create asynchronous single and multiple file uploads. All uploads are done into the uploads directory. In addition to the default functionality we need a possibility to show the preview of the temporary uploaded file, translate all messages and buttons, delete a file, move a file to a specific directory. I created a demo project which implements all that.

If you have a ModelForm with a FileField or ImageField, you need to not show this field in the form, but instead to add a hidden field for uploaded file path. When you choose a file, it will be uploaded to a temporary uploads directory and its path will be set in the hidden field. Also you need a hidden BooleanField for the state of file deletion. When you submit the form, the file will be moved from the temporary location to the correct location defined by the FileField or ImageField.

In the given example, besides django-ajax-uploader, I am using django-crispy-forms with bootstrap 3.0.0 support. It allows you to define the structure for the forms without creating repetitive HTML markup.

This would be a quick workflow of integrating ajax uploads into your project:

  • Install django-ajax-uploader and django-crispy-forms.
  • Put 'crispy_forms' and 'ajaxuploader' into INSTALLED_APPS.
  • Define CRISPY_TEMPLATE_PACK = 'bootstrap3' in the settings.
  • Define the url rule for ajax uploader
    from ajaxuploader.views import AjaxFileUploader
    uploader = AjaxFileUploader()
    urlpatterns = patterns('',
        # ...
        url(r'^helper/ajax-upload/$', uploader, name="ajax_uploader"),
        # ...
    )
    
  • Create a form for your model which will have the ajax uploader.
  • Create the view which will handle your model and the chosen files and call it in your urls.
  • Create the template with appropriate javascript.

For a working example, please check image uploads project.

2008-08-08

MultipleSubmitButton Widget for ChoiceField

Recently I published a snippet with a widget rendering a choice field as a series of submit buttons.

So the {{ form.do }} field from the following form:

SUBMIT_CHOICES = (
('save', _("Save")),
('save-add', _("Save and Add Another")),
)

class TestForm(forms.Form):
do = forms.ChoiceField(
widget=MultipleSubmitButton,
choices=SUBMIT_CHOICES,
)



will be rendered as:

<ul>
<li><button type="submit" name="do" value="save">Save</button></li>
<li><button type="submit" name="do" value="save-add">Save and Add Another</button></li>
</ul>


Can somebody enhance this widget so that it supports iteration through different choices and getting specific buttons by indexes in the template? My trials failed, but maybe you will succeed!