instance method conditions_tables

# File activerecord/lib/active_record/associations.rb, line 1723
        def conditions_tables(options)
          # look in both sets of conditions
          conditions = [scope(:find, :conditions), options[:conditions]].inject([]) do |all, cond|
            case cond
              when nil   then all
              when Array then all << tables_in_string(cond.first)
              when Hash  then all << tables_in_hash(cond)
              else            all << tables_in_string(cond)
            end
          end
          conditions.flatten
        end