Add a quick note about :select and eagerly included associations. [Rick]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4363 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
+* Add a quick note about :select and eagerly included associations. [Rick]
+
 * Add docs for the :as option in has_one associations.  Closes #5144 [cdcarter@gmail.com]
 
 * Fixed that has_many collections shouldn't load the entire association to do build or create [DHH]

activerecord/lib/active_record/associations.rb

@@ -348,7 +348,8 @@ def clear_association_cache #:nodoc:
     #
     # Also have in mind that since the eager loading is pulling from multiple tables, you'll have to disambiguate any column references
     # in both conditions and orders. So :order => "posts.id DESC" will work while :order => "id DESC" will not. This may require that
-    # you alter the :order and :conditions on the association definitions themselves.
+    # you alter the :order and :conditions on the association definitions themselves.  Because eager loading generates the SELECT statement too,
+    # the :select option is ignored.
     #
     # It's currently not possible to use eager loading on multiple associations from the same table. Eager loading will not pull
     # additional attributes on join tables, so "rich associations" with has_and_belongs_to_many is not a good fit for eager loading.