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

In Rails4:

class Post < ActiveRecord::Base 
  has_and_belongs_to_many :tags, -> { uniq }

(beware, the -> { uniq } must be directly after the relation name, before other params)

Rails documentation