[wp-hackers] Capabilities as a taxonomy

Otto otto at ottodestruct.com
Fri Jan 22 16:48:58 UTC 2010

On Fri, Jan 22, 2010 at 10:23 AM, Andrew Nacin <wp at andrewnacin.com> wrote:
> Actually, that still exists.
> The current system allows for a single user to have multiple roles and
> overriding individual capabilities as well. What has been proposed is
> limiting users to a single role with no opportunity for individual
> capabilities on top of that.

I'm okay with eliminating individual capabilities, but we really
should keep multi-role. I can envision a system where you separate
"writers" from "editors" and have a role just for "comment moderators"
and so forth. It would make more sense to assign one user to multiple
roles than to make combined roles just for them.

If performance is a problem, then we need to look at redesigning to
make it not a problem. However I don't think that means we should give
up the more obvious and useful configuration abilities.

The most common case is probably going to be "does user A have
capability X?". So optimize for that and other common query cases.
It's unlikely we'll need a system that can also do "what users have
capability X?", because that's not something you would normally care
about. You'd be more likely to ask "what are the roles all the users
are in?" and similar.

Define your use cases, optimize the design for those.

The main cases I see are:
"does user A have capability X?"
"what roles does user A have?"
"what capabilities does role R have?"

Given this, I'd probably make the roles into usermeta fields (_role?),
and make the capabilities into terms in a taxonomy, linking them to
role names. User has role AAA, and a taxonomy exists with AAA or
something as the name of it. Terms like "can_edit_posts" and similar
are related to that role.

Pulling a user's roles is then a simple meta lookup. Pulling all terms
for a taxonomy is one select, joining the terms to the relationships
and taxonomy (same as tags/categories). Checking a single capability
on a user is a combination of the two. If role names match taxonomy
names, that's a single select as well (albeit with a lot of joining).
Might want to make role names be forced to have a hidden prefix or
something to make this unlikely to interfere with other custom

If you want to reverse the process, it's a bit more difficult, but not
crazily so. "What users have capability X?" would be a) Find the term
for that capability, joined to relationships to see which taxonomies
it's in. This gives you the role names. Then b) select the usermeta
where _role in roles to get the list of user ids.

Sent from Memphis, TN, United States

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