Currently there is no way to populate has_and_belongs_to_many because there is no model set apart for the join table. There should be additional methods one can call on either side of the association to setup the join.

Sometimes it's not applicable to do a loop because it is limited in how the nesting works. Instead one should be able to build up an array of hashes and assign it in one call.

Item.populate [{:name => "foo"}, {:name => "bar"}]