Render template parts with extended cache control.

Installation

Install django-viewlet in your python environment

$ pip install django-viewlet

Supports Django versions 2.2, 3.2, 4.0 and Python versions 3.7 - 3.9.

Configuration

Add viewlet to your INSTALLED_APPS setting so Django can find the template tag

INSTALLED_APPS = (
    ...,
    "viewlet",
)

Jinja2

Add ViewletExtension to the list of extensions of Jinja2 template engine

TEMPLATES = (
    [
        {
            "BACKEND": "django.template.backends.jinja2.Jinja2",
            # ...
            "OPTIONS": {
                # ...
                "extensions": [
                    # ...
                    "viewlet.loaders.jinja2_loader.ViewletExtension",
                ],
            },
        }
    ],
)

Usage

A viewlet is almost like a function based django view, taking a template context as first argument instead of request. Place your viewlets in viewlets.py or existing views.py in your django app directory.

from django.template.loader import render_to_string
from viewlet import viewlet


@viewlet
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

You can then render the viewlet with the viewlet template tag:

{% load viewlets %}
<p>{% viewlet hello_user request.user.username %}</p>

... and in your Jinja2 templates:

<p>{% viewlet 'host_sponsors', host.id) %}</p>

Specifying cache backend

By default viewlet will try using viewlet cache alias, falling back to default. You can specify which alias should be used in settings:

VIEWLET_DEFAULT_CACHE_ALIAS = "template_cache"

CACHES = {
    # ...
    "template_cache": {
        # ...
    },
    # ...
}

Additionally, you can override cache alias in viewlet decorator with using argument

@viewlet(using="super_cache")
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

Refreshing viewlets

A cached viewlet can be re-rendered and updated behind the scenes with viewlet.refresh

import viewlet

viewlet.refresh("hello_user", "monkey")
# or
hello_user.refresh("monkey")

The decorator

@viewlet(name, template, key, timeout)
def my_viewlet():
    ...

• name

  Optional reference name for the viewlet, defaults to function name.

• template

  Optional path to template. If specified the viewlet must return a context dict, otherwise it is responsible to return the rendered output itself.

• key

  Optional cache key, if not specified a dynamic key will be generated viewlet:name(args...)

• timeout

  Cache timeout. Defaults to configured cache backend default timeout, None = eternal, 0 = uncached.

Examples

The content returned by the viewlet will by default be cached. Use the timeout argument to change this.

@viewlet(timeout=30 * 60)
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

Tip: Set timeout to None to cache forever and use viewlet.refresh to update the cache.

Django viewlet will by default build a cache key viewlet:name(args...). To customize this key pass a string to the viewlet decorator argument key that includes string mod operators for each viewlet argument.

@viewlet(timeout=30 * 60, key="some_cache_key_%s")
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

Django viewlet will cache returned context instead of html by using the template decorator argument. This is useful if cached html is too heavy, or your viewlet template needs to be rendered on every call. The specified template will then be rendered with the viewlet context merged with the parent context, usually a RequestContext.

@viewlet(template="hello_user.html", timeout=30 * 60)
def hello_user(context, name):
    return {"name": name}

Note: Return context dict for the template, not rendered html/text

If there is no need for caching, set the viewlet decorator argument timeout to 0.

@viewlet(timeout=0)
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

By default your viewlets will be named as the function. To override this you can set the decorator argument name

@viewlet(name="greeting")
def hello_user(context, name):
    return render_to_string("hello_user.html", {"name": name})

A powerful usage of viewlet.refresh is to use it together with Django signals:

class Product(Model):
    name = CharField(max_length=255)


@viewlet(timeout=None)
def product_teaser(context, id):
    product = get_context_object(Product, id, context)
    return render_to_string("product_teaser.html", locals())


def refresh_product_teaser(instance, **kwargs):
    viewlet.refresh("product_teaser", instance.id)


post_save.connect(refresh_product_teaser, Product)

Viewlets can also be accesses with AJAX by adding viewlet.urls to your Django root urls:

urlpatterns = patterns(
    "",
    (r"^viewlet/", include("viewlet.urls")),
)

The url ends with the viewlet name followed by a querystring used as kwargs to the viewlet:

http://localhost:8000/viewlet/[name]/?arg=1...