6 Apr
2012
6 Apr
'12
10:17 a.m.
Actually, another way of presenting your proposal in a more generic way would be:
"Add support for component Aliases".
It's slightly more generic since it's not just about default. If you wish to
change a hint for another one because it's not well named you could do it through an
alias.
This would also mean adding a ComponentManager.setAlias(String alias, Type existingRole,
String existingHint).
Anyway, the next step IMO is to check what Guice/CDI and OSGi are doing in this regards.
Thanks
-Vincent
On Apr 5, 2012, at 5:55 PM, Sergiu Dumitriu wrote:
Hi devs,
Currently, requesting a component instance without a hint will look for the
implementation that uses the "default" hint, which makes it difficult to change
the implementation in an XWiki instance. Sure, it is easy as long as all the
implementations use the "default" hint, but choosing the default between
alternative implementations that should all still be usable by themselves is not
possible.
Also, "default" is not really a good hint, since it describes the state of the
implementation, not the technology, the aspect that makes it different from the others. It
would be better to name each implementation with a proper hint.
I propose to define a mapping that can specify which hint is the default for a component.
In a text file, META-INF/component-defaults.txt, we'll keep
componentinterface=defaulthint mappings. For example:
com.xpn.xwiki.store.XWikiStoreInterface=hibernate
com.xpn.xwiki.store.migration.DataMigrationManager=hibernate
And then, when we lookup the current storage implementation, we don't need to check
what is the configured hint in xwiki.cfg (or xwiki.properties), we can just request the
default implementation.
If there's no mapping for a component, we'll continue to use the
"default" hint.
I'm not sure where exactly to keep such files. We bundle a components.txt file in
each jar containing component implementations. We could do the same for the components we
consider the platform defaults, and allow overrides in the
WEB-INF/classes/META-INF/component-defaults.txt file. Still, this means that whenever
platform defaults change, we need to keep another special section in the release notes, to
let users know about these changes, so that they can manually revert to the old default if
they need to.
In the future we could change existing components to give proper hints instead of
"default", where such a change is applicable.
Another idea is to not use "default" at all, and instead go for a generic
"xwiki", "xe", "xwiki-platform" or something like that
whenever there's just one implementation for a component and we can't find another
hint to describe it.
WDYT?
--
Sergiu Dumitriu