Hi folks,
I think Daniel buried the lede here (see his mail below), so I'm
mailing this out with a subject line that will hopefully provoke more
discussion. :-)
This is an RFC we originally conceived at the Hong Kong Wikimania
architecture discussion. The notes from that are here:
https://www.mediawiki.org/wiki/Architecture_guidelines/Meetings/Wikimania_2…
There has been discussion on this RFC here, so far only between Tim and Daniel:
https://www.mediawiki.org/wiki/Talk:Requests_for_comment/TitleValue
It would be good to get some other voices in that conversation.
Rob
---------- Forwarded message ----------
From: Daniel Kinzler <daniel(a)brightbyte.de>
Date: Tue, Oct 1, 2013 at 10:18 AM
Subject: [Wikitech-l] RFC: TitleValue
To: Wikimedia developers <wikitech-l(a)lists.wikimedia.org>
[Re-posting, since my original post apparently never got through. Maybe I posted
from the wrong email account.]
Hi all!
As discussed at the MediaWiki Architecture session at Wikimania, I have created
an RFC for the TitleValue class, which could be used to replace the heavy-weight
Title class in many places. The idea is to show case the advantages (and
difficulties) of using true "value objects" as opposed to "active
records". The
idea being that hair should not know how to cut itself.
You can find the proposal here:
<https://www.mediawiki.org/wiki/Requests_for_comment/TitleValue>
Any feedback would be greatly appreciated.
-- daniel
PS: I have included the some parts of the proposal below, to give a quick
impression.
------------------------------------------------------------------------------
== Motivation ==
The old Title class is huge and has many dependencies. It relies on global state
for things like namespace resolution and permission checks. It requires a
database connection for caching.
This makes it hard to use Title objects in a different context, such as unit
tests. Which in turn makes it quite difficult to write any clean unit tests (not
using any global state) for MediaWiki since Title objects are required as
parameters by many classes.
In a more fundamental sense, the fact that Title has so many dependencies, and
everything that uses a Title object inherits all of these dependencies, means
that the MediaWiki codebase as a whole has highly "tangled" dependencies, and
it
is very hard to use individual classes separately.
Instead of trying to refactor and redefine the Title class, this proposal
suggest to introduce an alternative class that can be used instead of Title
object to represent the title of a wiki page. The implementation of the old
Title class should be changed to rely on the new code where possible, but its
interface and behavior should not change.
== Architecture ==
The proposed architecture consists of three parts, initially:
# The TitleValue class itself. As a value object, this has no knowledge about
namespaces, permissions, etc. It does not support normalization either, since
that would require knowledge about the local configuration.
# A TitleParser service that has configuration knowledge about namespaces and
normalization rules. Any class that needs to turn a string into a TitleValue
should require a TitleParser service as a constructor argument (dependency
injection). Should that not be possible, a TitleParser can be obtained from a
global registry.
# A TitleFormatter service that has configuration knowledge about namespaces and
normalization rules. Any class that needs to turn a TitleValue into a string
should require a TitleFormatter service as a constructor argument (dependency
injection). Should that not be possible, a TitleFormatter can be obtained from a
global registry.
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