destroy_all, with conditions.

gistfile1.txt

> # on a model, works fine.
> Voucher.destroy_all(:user_id => nil)
=> # works as expected; returns an array of the records it destroyed, and said records have been deleted.

> # on a collection:
> wv.voucher_restrictions.destroy_all(:restriction_id => 108)
=> ArgumentError: wrong number of arguments (1 for 0)

> # but... this works:
> wv.voucher_restrictions.where(:restriction_id => 108).destroy_all