Question

I’m working on rails application with postgres db.I have a table called merchant_review_votes where schema is

--------------------------------------------------
 id                  | integer 
 user_id             | integer 
 merchant_review_id  | integer
 value               | integer
 created_at          | timestamp without time zone
 updated_at          | timestamp without time zone
--------------------------------------------------

I’m creating a another section(say products) which involve voting is it a good idea to create another schema similar to this or modify the code and use just one table.
If just one table how will the schema look?. What kinda problems i can face..

Answer 1

This sounds like a good case for a Polymorphic Association.

class Review < ActiveRecord::Base
  belongs_to :user
  belongs_to :reviewable, :polymorphic => true
end

class Merchant < ActiveRecord::Base
  has_many :reviews, :as => :reviewable
end

class Product < ActiveRecord::Base
  has_many :reviews, :as => :reviewable
end

You can then call @merchant.reviews and @product.reviews to get the reviews of merchants and products, respectively. And you can call @review.reviewable to get the object that was reviewed.

The polymorphic association is based on a table structure like this:

--------------------------------------------------
  id                  | integer 
  user_id             | integer 
  reviewable_id       | integer
  reviewable_type     | string
  value               | integer
  created_at          | timestamp without time zone
  updated_at          | timestamp without time zone
--------------------------------------------------

The reviewable_type column holds the class name of the “reviewable” object and the reviewable_id holds it’s id. In a migration you can create these columns using:

 t.references :reviewable, :polymorphic => true