best-practices.rst

Best practices for writing CKAN themes

Don't use c

As much as possible, avoid accessing the Pylons template context :pyc (or :pytmpl_context). :pyc is a thread-global variable, which encourages spaghetti code that's difficult to understand and to debug.

Instead, have controller methods add variables to the :pyextra_vars parameter of :py~ckan.lib.base.render, or have the templates call template helper functions <template-helper-functions> instead.

:pyextra_vars has the advantage that it allows templates, which are difficult to debug, to be simpler and shifts logic into the easier-to-test and easier-to-debug Python code. On the other hand, template helper functions are easier to reuse as they're available to all templates and they avoid inconsistencies between the namespaces of templates that are rendered by different controllers (e.g. one controller method passes the package dict as an extra var named package, another controller method passes the same thing but calls it pkg, a third calls it pkg_dict).

You can use the :py~ckan.plugins.interfaces.ITemplateHelpers plugin interface to add custom helper functions, see custom template helper functions.

Use url_for()

Always use :py~ckan.lib.helpers.url_for (available to templates as h.url_for()) when linking to other CKAN pages, instead of hardcoding URLs like <a href="/dataset">. Links created with :py~ckan.lib.helpers.url_for will update themselves if the URL routing changes in a new version of CKAN, or if a plugin changes the URL routing.

Use {% trans %}, {% pluralize %}, _() and ungettext()

All user-visible strings should be internationalized, see /contributing/string-i18n.

Avoid name clashes

See avoid name clashes.

modules should have docstrings

A module should have a docstring at the top of the file, briefly documentating what the module does and what options it takes. For example:

/../ckanext/example_theme_docs/v17_popover/fanstatic/example_theme_popover.js

JavaScript modules should unsubscribe from events in teardown()

Any JavaScript module that calls :jsthis.sandbox.client.subscribe should have a teardown() function that calls :js~this.sandbox.client.unsubscribe, to prevent memory leaks. CKAN calls the teardown() functions of modules when those modules are removed from the page.

Don't overuse pubsub

There shouldn't be very many cases where a JavaScript module really needs to use Pubsub <pubsub>, try to only use it when you really need to.

JavaScript modules in CKAN are designed to be small and loosely-coupled, for example modules don't share any global variables and don't call each other's functions. But pubsub offers a way to tightly couple JavaScript modules together, by making modules depend on multiple events published by other modules. This can make the code buggy and difficult to understand.

Use {% snippet %}, not {% include %}

Always use CKAN's custom {% snippet %} tag instead of Jinja's default {% include %} tag. Snippets can only access certain global variables, and any variables explicitly passed to them by the calling template. They don't have access to the full context of the calling template, as included files do. This makes snippets more reusable, and much easier to debug.

Snippets should have docstrings

A snippet should have a docstring comment at the top of the file that briefly documents what the snippet does and what parameters it requires. For example:

/../ckanext/example_theme_docs/v10_custom_snippet/templates/snippets/example_theme_most_popular_groups.html