Cached .all(:include=>[:xxx]) on associations

When fetching all associations with includes they are not cached, but could be, since they are still the same records(unlike with :select/:conditions etc)

user = User.first
user.comments.length # hits db
user.comments.length # cached

user = User.first
user.commens.all(:include=>:comenter).length  # hits db
user.commens.all(:include=>:comenter).length  # hits db
user.comments.length # hits db

Cached find all with includes
This can save requests when performing repetitive calls to the same record.

user = User.first
user.comments.load_target_with_includes([:commenter, :tags]).length # hits db
user.comments.load_target_with_includes([:commenter, :tags]).length # cached
user.comments.length # cached


# do not load an association twice, when all we need are includes
# all(:include=>xxx) would always reload the target
class ActiveRecord::Associations::AssociationCollection
  def load_target_with_includes(includes)
    raise if @owner.new_record?

    if loaded?
      @loaded = true
      @target = all(:include => includes)

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