ruby on rails - Define variable in model method -

i'm getting keywords array html form different keywords. need put them string value keyword1,keyword2,keyword3.

the problem keywords_line string. see has value inside of .each cycle has not out of it. how set keywords_line work correctly?

  # models/item.rb   before_save :create_slug_and_keywords    def create_slug_and_keywords      if defined? self.keywords       self.keywords.each |k|         if defined? keywords_line           keywords_line = keywords_line + ',' + k         else            keywords_line = k         end        end        if defined? keywords_line # keywords_line not defined here         keywords = keywords_line       else          keywords = nil       end     end 

if keywords array, self.keywords.join(',')

and link doc.

http://ruby-doc.org/core-1.8.7/array.html#method-i-join