Thanks to a great suggestion by Josh Susser. I've spent the past two days completely re-working the code I submitted in the eariler patch.
The new patch; http://dev.rubyonrails.org/ticket/10012 accomplishes the same results, but with a much better api.
The earlier patch added a new option for use with :include which named associated AR classes not to be eagerly loaded. This negative specification was awkward.
At Josh's suggestion, the new patch extends the values acceptable to the existing :joins option. If a string it used things will work as before. If not, the values take the same form as values for :include, i.e. symbols, hashes, and arrays of symbols and hashes. These are used to construct a join clause for the sql query, and the same code used to process the results for the :include option, patched to be aware of these new active record joins, instantiates the result objects, stripping out the extra attributes from the join, so that the results are writable (unlike those returned from :joins with a string value.
This allows you to add tables to a query for use in the conditions, but not instantiate unneeded associated objects when they will not (all) be needed. In addition since this generates a regular inner join rather than the left outer join generated by :include, less data may be returned to be processed in cases where there are records with missing associated records.
I look forward to feedback.
