In your example, you could just inherit from generic-list.html since it already
extends base.html. You would be repeating yourself in your current example.
orders/list.html
{% extends 'generic-list.html' %}
{% block list-item %}
<li>Order # {{ order.id }} (total: {{ order.total }})</li>
{% endblock %}
From: [email protected]
[mailto:[email protected]] On Behalf Of Yo-Yo Ma
Sent: Sunday, February 16, 2020 10:02 AM
To: Django developers (Contributions to Django itself)
Subject: Proposal: Multiple-Inheritance in Templates
Please read this in full - you will not be disappointed by the end.
We often talk about "multiple-inheritance" when referring to multiple levels of
{% extends ... %} and defining {% block ... %} many layers up in base templates.
But, something that comes up as a useful idea in my mind on a regular basis
when working in Django templates is the ability to actually inherit from
multiple base templates.
The immediate reaction to this idea might be repulsion until you think through
the implications and weigh them against the benefits.
An example (simplified) use case speaks louder than explanation:
base.html
<a>Some top-level menu</a>
{% block submenu %}{% endblock %}
{% block content %}{% endblock %}
--
orders/base.html
{% extends 'base.html' %}
{% block submenu %}
<a>View all Orders</a>
<a>Enter an Order</a>
{% endblock %}
--
products/base.html
{% extends 'base.html' %}
{% block submenu %}
<a>View all Products</a>
<a>Create a Product</a>
{% endblock %}
--
So, we have a relatively common template setup, with some apps defining their
own base templates that extend the main base template, and then defining their
own submenus, etc.
At this point, we know there will be a product list page and an order list
page, but we also know that the product list template will extend the product
base template and the order list template will extend the order base template;
same goes for the product create and order create, both also extending their
respective apps' base templates.
This means duplication. The product list template will contain most of the same
list-related HTML, etc. as the order list, but the only way to avoid that
duplication will be to make a base list template and extend that template from
both the product list and order list.
generic-list.html
{% extends 'base.html' %}
{% block content %}
<ul>
{% for object in page.object_list %}
{% block list-item %}
<li>{{ object }}</li>
{% endblock %}
{% endfor %}
</ul>
{% endblock %}
--
But, in this case we lose the benefit of the product base and order base (the
submenus they define). Submenus are a super simplified example, but in reality
there may be *many* different things about a given app's base template, making
it a dilemma, or simply removing the practical ability to subclass a "generic
list" template altogether.
Introducing multiple-inheritance:
orders/list.html
{% extends 'generic-list.html 'orders/base.html' %}
{% block list-item %}
<li>Order # {{ order.id }} (total: {{ order.total }})</li>
{% endblock %}
--
products/list.html
{% extends 'generic-list.html 'products/base.html' %}
{% block list-item %}
<li>Product # {{ product.id }} (price: {{ product.price }})</li>
{% endblock %}
--
The order of the templates would define the order of block definition and
override precedence, from left to right (similar to Python class MRO).
You can also see, by the overriding of the "list-item" block, that there are
other benefits of using extension like this, compared to e.g., defining a list
template as an include, as a workaround.
Each template in the list would need to extend from template at the very right,
meaning that each template left of the main template would essentially be a
mixin. This would solve the very real problem of making generic bases for types
of templates (list, detail, form, etc.) in your app, while still preserving the
benefits of extension (block overrides) to all other facets of your final
templates (vs having to use includes).
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