Django template language

Template Tags

Django template tags are keywords that allow you to perform some programming logic in your templates, such as if statements, for loops, variables, filters, etc. They are surrounded by {% %} brackets. Some examples of built-in template tags are:

• {% extends "base.html" %}: inherits from another template
• {% block content %}...{% endblock %}: defines a block that can be overridden by child templates
• {% include "navbar.html" %}: includes another template as part of this template
• {% if user.is_authenticated %}...{% endif %}: checks a condition and displays different content accordingly
• {% load static %}: This feature is used to load static files (like CSS or JavaScript files) into your Django templates.
• {% for item in items %} and {% endfor %}: Allows you to iterate over a list or other iterable and render a block of content for each item.
• {% for fossil in fossils %}{{ fossil.fossil_name }}{% empty %}No fossils{% endfor %}: Display default value if the queryset is empty.

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Custom Template Tags

You can create three types of custom template tags using helper functions provided by Django:

• simple_tag: processes some data and returns a string that is displayed in the template
• inclusion_tag: processes some data and returns a rendered template that is included in the template
• assignment_tag: processes some data and sets a variable in the context that can be used later in the template

Create a custom tag:

• Create a templatetags directory inside your app directory, and add an __init__.py file to it so that Django recognizes it as a Python package
• Create a module (my_tags.py) inside the templatetags directory, and import template from django
• Define your custom tag function using one of the helper functions (simple_tag, inclusion_tag, or assignment_tag) as a decorator, and register it with template.Library()

from django import template

register = template.Library()

@register.simple_tag
def add(a, b):
    return str(a + b)

• Load your custom tag module in your templates using {% load my_tags %} before using your custom tag

{% load my_tags %}
    <p>The sum of 2 and 3 is {% add 2 3 %}.</p>

Example

Template tags can be used to access model data without creating views. This data is available for all templates, even base.html or navbar.html.

Create a new module in the templatetags directory

• app_fossils
  • templatetags
    • __init__.py
    • app_extras.py

Update the app_extras.py file

from django import Template
from django.db import models
from app.models import ModelToAccess

register = template.Library()

@register.simple_tag
def all_fields():
    return ModelToAccess.objects.all()

HTML templates:

{% load app_extras %} 
{% all_fields as fields%} 
{% for field in fields %}{{ field .selected_model_field }} <br>{% endfor %}

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Core Functions

Default if False

{{ value|default:"nothing" }}

Default if none

{{ value|dictsort:"name" }}

Lists and strings

Allow new lines in text areas in templates

{{ value|linebreaks }}

Return first item

{{ value|first }}

Return last item

{{ value|last }}

Return random item

{{ value|random }}

Return length of list or string

{{ value|length }}

Check if length of list or string is

{{ value|length_is:"4" }}

Pluralize

You have {{ num_messages }} message{{ num_messages|pluralize }}. OR You have {{ num_walruses }} walrus{{ num_walruses|pluralize:"es" }}.

Create slices of text

{{ some_list|slice:":200" }}

Create slices of lists

{{ some_list|slice:":2" }}

All string in lowercase

{{ value|lower }}

Capitalize first letter

{{ value|capfirst }}

Capitalize all first letters in a sentence

{{ value|title }}

Capitalize all letters

{{ value|upper }}

Wrap words after specific number of letters

{{ value|wordwrap:5 }}

Remove values from string (in this example all spaces)

{{ value|cut:" " }}

Center text between number of spaces

"{{ value|center:"15" }}"

Count words

{{ value|wordcount }}

Time

Now

{% now "Y.m.d H:i" %}

Date

{{ value|date:"Y m d" }}

Time

{{ value|time:"H:i" }}

Time since

{{ blog_date|timesince:comment_date }}

Time until

{{ conference_date|timeuntil:from_date }}

Numbers

Add

{{ value|add:"2" }}

Float format (34.23234 will become 34.23)

{{ value|floatformat:2 }}