has_and_belongs_to_many, avoiding dupes in the join table

Question

I have a pretty simple HABTM set of models

class Tag < ActiveRecord::Base 
   has_and_belongs_to_many :posts
end 

class Post < ActiveRecord::Base 
           


        

Answer 1

I worked around this by creating a before_save filter that fixes stuff up.

class Post < ActiveRecord::Base 
   has_and_belongs_to_many :tags
   before_save :fix_tags

   def tag_list= (tag_list) 
      self.tags.clear 
      tag_list.strip.split(' ').each do 
        self.tags.build(:name => tag) 
      end
   end  

    def fix_tags
      if self.tags.loaded?
        new_tags = [] 
        self.tags.each do |tag|
          if existing = Tag.find_by_name(tag.name) 
            new_tags << existing
          else 
            new_tags << tag
          end   
        end

        self.tags = new_tags 
      end
    end

end

It could be slightly optimised to work in batches with the tags, also it may need some slightly better transactional support.