Django Layers

Travis

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Django Layers makes it possible to serve a set of templates and static resources as defined in settings.py. This means you can serve different HTML, Javascript and CSS to eg. basic mobile devices, smart phones and desktop browsers. These template sets (aka layers) also stack, so if you create foo.html for basic devices it is automatically available for desktop browsers as well. You can override foo.html for desktop browsers.

Installation

1. Install or add django-layers-hr to your Python path.
2. Add layers after django.contrib.static to your INSTALLED_APPS setting.
3. Ensure the app that you will be creating layers for appears first in INSTALLED_APPS else template override won't work.
4. Add crum.CurrentRequestUserMiddleware to MIDDLEWARE.

Example

Note: there is a working example in the example subdirectory.

We have sites example.com, basic.example.com and smart.example.com. Each of the sites have their own settings.py, thus different Django processes.

Directory structure

templates
    - basic
        - foo.html (1)
        - bar.html (2)
    - smart
        - bar.html (3)
    - web
        - bar.html (4)

static
    - basic
        - foo.css (5)
        - bar.css (6)
    - smart
        - bar.css (7)
    - web
        - bar.css (8)

Settings

We define an "inheritance" hierarchy using a list-of-lists notation.

Two lines of inheritance: basic-smart and basic-web:

LAYERS = {'tree': ['basic', ['smart'], ['web']]}

One lines of inheritance: basic-smart-web.:

LAYERS = {'tree': ['basic', ['smart', ['web']]]}

There are two ways to configure layer lookup for system: specify the current layer in a settings file or look it up from the request. Omit the current key to enable request based lookups:

LAYERS = {'tree': ['basic', ['smart'], ['web']], 'current': 'web'}

Legacy settings require layers to be defined in separate settings files. The example below means we have three settings files, and thus three Django processes. Please migrate to the default tree format.

• Desktop settings has LAYERS = {'layers': ['basic', 'web']}.
• Basic settings has LAYERS = {'layers': ['basic']}.
• Smart settings has LAYERS = {'layers': ['basic', 'smart']}.

Add the loaders and finders to settings. The order is important.

INSTALLED_APPS = (
    'myapp',
    'layers',
    ...
)

TEMPLATE_LOADERS = (
    'layers.loaders.filesystem.Loader',
    'django.template.loaders.filesystem.Loader',
    'layers.loaders.app_directories.Loader',
    'django.template.loaders.app_directories.Loader',
)

STATICFILES_FINDERS = (
    'layers.finders.FileSystemFinder',
    'django.contrib.staticfiles.finders.FileSystemFinder',
    'layers.finders.AppDirectoriesFinder',
    'django.contrib.staticfiles.finders.AppDirectoriesFinder',
)

Template results

• http://example.com/foo yields (1).
• http://example.com/bar yields (4).
• http://basic.example.com/foo yields (1).
• http://basic.example.com/bar yields (2).
• http://smart.example.com/foo yields (1).
• http://smart.example.com/foo yields (3).

Static results

• http://example.com/static/foo.css yields (5).
• http://example.com/static/bar.css yields (8).
• http://basic.example.com/static/foo.css yields (5).
• http://basic.example.com/static/bar.css yields (6).
• http://smart.example.com/static/foo.css yields (5).
• http://smart.example.com/static/foo.css yields (7).

Overriding templates from other apps

The normal template resolution rules apply. Creating eg. templates/web/registration/login.html will override the login page for web only.

Collectstatic

Collectstatic remains unaffected. The collector delegates to finders, so all layer aware resources end up with partial paths under the STATIC_ROOT directory.

Decorators

A user could follow a link that leads him to a layer that serves a broken page. For example a web site is served on www.site.com with an accompanying basic site m.site.com. Visiting www.site.com/flashy-dashboard with a basic device like a Samsung E250 will result in the user being redirected to m.site.com/flashy-dashboard. That page probably does not exist for basic devices because it can't render it well enough. In such a case a decorator exclude_from_layers is provided that renders a friendly page instead of a 404 or 500 error:

class WebOnlyView(TemplateView):
    template_name = "layers/web_only_view.html"

    @exclude_from_layers(layers=("basic",))
    def get(self, *args, **kwargs):
        return super(WebOnlyView, self).get(*args, **kwargs)

Request based layer lookup

The preferred way of layer lookup is through the presense of an X-Django-Layer header in the request. Django Layers layer lookup is very similar to the site object lookup done in django.contrib.sites. If a layer is explicitly defined in settings then that is used, else the request headers are inspected.

During development you will likely define the layer in your settings file, but in a production environment you don't want a Django process per layer, so request based lookups are preferred.

Layer objects

The management command load_layers creates a Layer object for each layer in your project. It is useful for doing layer based filtering at database level.

Can I add my own layers?

Yes! Basic, smart and web are just examples. You can define any hierarchy with any names.