@specific_feeling_posts = @posts.feeling.where(:feeling => "happy")

class Post < ActiveRecord::Base
  has_many :feelingships
  has_many :feelings, :through => :feelingships
  belongs_to :user
end

class Feeling < ActiveRecord::Base
  has_many :feelingships
  has_many :posts, :through => :feelingships
end

class Feelingship < ActiveRecord::Base
  belongs_to :post
  belongs_to :feeling
end

@happy_posts = Post.joins(:feelings).where("feelings.title = ?", "happy")

@specific_feelings_post=Post.join(:feelings).where("feelings.title= ?","specific_feeling")