Alternative to merge_conditions in Rails 3

merge_conditions seems to be gone from rails 3. Is there something in
Rails 3 or Arel that would allow me to achieve the same thing, which
is to merge various types of conditions (array, hash, etc)? I haven't
spent much time with Arel, so I may be missing something obvious.

Thanks

I've had luck with doing this:

Post.where(:comments => {author_id => 1}).where(:title => 'How to
specify nested conditions')

This seems to replace the need for merge_conditions.