ruby on rails - undefined method 'article' - use data from other model -

there articles , comments.

article has_many :comments comment belongs_to :article 

i want comments value_id equal value_id attribute in article comment belongs_to.

class comment < activerecord::base    belongs_to :article    def self.value_comments     where(value_id: self.article.value_id)   end  end 

i error:

undefined method `article' #<class:0x007fd2a7e46d18> 

controller

@value_comments = comment.value_comments.where(user_id: current_user.id).order("created_at desc") 

having read question again, understanding want find comments value_id matches value_id of associated article.

your code correct - need few more parts work. need join comment table article table using joins. then, refer column in function using arel_table.

so should end this:

def self.value_comments   joins(:article).where(self.arel_table[:value_id].eq article.arel_table[:value_id]) end 

you consider using sexy_scopes make easier access columns.