[ckan-dev] ordering of plugins

Tue May 31 17:34:54 UTC 2011

Great stuff.

I think the whole extension system could do with a bit more discussion
some time soon.  I think it's a great start but can think of various
improvements.  For example (and this may be controversial), it would
be nice for the configuration to live in the database, so a site
administrator can edit it.  The same place would have a concept of
active and inactive modules so that there's a place to prompt admins
to fill out stuff post-install, and we have the possibility of a nice
failure mode.

An alternative would be something like apache's module system.  Each
extension has an ini file that it drops in a known location
(extensions-available.d/).  Enabling them is a matter of editing their
ini file and symlinking it to extensions-enabled.d/.

This would make extension configuration management much easier.

Seb

On 31 May 2011 17:47, David Read <david.read at okfn.org> wrote:
> Hi folks,
>
> David Raznick and I have been discussing CKAN plugins and worrying
> about the order that they run in. I've done a bit of digging and have
> added a section to the plugin docs - see below. In summary, the order
> is the same for every run, and is determinable, although alphabetical
> is not ideal and may need improving on in the future.
>
> David
>
> Ordering of extensions
> ~~~~~~~~~~~~~~~~~~~~~~
>
> .. caution ::
>
>  The order that extensions are initially loaded is **different** to
> the order that their plugins are run.
>
> The order that extensions are initially loaded is as follows:
>
> 1. System plugins (in setup.py under ``ckan.system_plugins``).
>
> 2. In order of the plugins specified in the config file: ``plugins =``.
>
> 3. If more than one module has a plug-in with the same name specified
> in the config, then all those are loaded, in the order the modules
> appear in ``sys.path``.
>
> The order that a plugins are run in, for example the order that
> IRoutes extensions have their ``before_map`` method run, is
> alphabetical by the plugin class.
>
> e.g. here is the order for these four extensions: ``<Plugin
> DguInventoryPlugin>``, ``<Plugin FormApiPlugin>``, ``<Plugin
> StatsPlugin>``, ``<Plugin WalesThemePlugin>``
>
> (This alphabetical ordering is done by
> ``pyutilib.component.core:ExtensionPoint.extensions()``)
>
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