How to delete polymorphic models cascade

If you use a polymorphic model in your Rails application, like in example

class Trade < ActiveRecord::Base

  has_many :gl_entries, as: :source, dependent: :destroy

end



class GlEntry < ActiveRecord::Base

  belongs_to :source, polymorphic: true

end

You will not be able to add the usual foreign keys for cascading delete records. But this can be implemented using a database.

To do this, you need to write a trigger in the database that will run the delete function for each record.

CREATE FUNCTION deleteGlEntriesOfTrade()

  RETURNS TRIGGER

  SET SCHEMA 'public'

  LANGUAGE plpgsql 

  AS $$

  BEGIN

    DELETE FROM gl_entries WHERE source_id = OLD.id AND source_type = 'Trade';

    RETURN OLD;   

  END;

  $$;



CREATE TRIGGER deleteTradesGlEntriesTrigger 

  BEFORE DELETE ON trades

  FOR EACH ROW EXECUTE PROCEDURE deleteGlEntriesOfTrade();

Create a migration and use :)