[DDC-217] Cache SQL results before hydration (and not after).

[sobstel]

I've made my own implementation for this:
https://github.com/sobstel/doctrine2/commit/f583625f791da22dec77dd7d6c83b813f0bcbdaa
There are no changes in specific hydrators and there is no fetchAll(). I've added 2 wrappers: one for cached result array, and one for uncached pdo statement. The former (CachedResultStatement) is actually ArrayIterator which just implements used methods (fetch & closeCursor => also specified in ResultStatementInterface). The latter is decorator for stmt, which just collects results on each call of fetch() (results are later available by calling getResult), and apart from this all calls are delegated to actual stmt object.

I've used (copied) following changes from Daniel dcousineau@c23b5a9

Whole discussion: http://www.doctrine-project.org/jira/browse/DDC-217

[beberlei]

The idea we are now going with is an SQL cache at the Doctrine\DBAL\Connection level. This does not add another layer of complexity in the hydration/query layer.

[sobstel]

Nice, was thinking about using Connection for this but wasn't sure how to relate it with cache id. Btw, will it also include caching for data fetched via finders ($em->find()) as well as relations? Right now, there's no way to cache this at Doctrine level.