Rails - how to restrict user from entering more than one record per association

Question

I am new to rails and have not been able to find something for this.

In my app, I have Products, Reviews, & Users.

Reviews belongs_to users & products while both users and products "has_many" reviews.

However, I want to restrict users from entering multiple reviews per product (each product is unique). So if a user creates a review for a product and tries to write another review for the same product, they'd be told they are not allowed to but can edit their existing review.

My question is: Should I do this at the controller level, or is possible to do it with a validation (which seems like a simpler solution)? Just not sure how to approach it.

Answer 1

You can easily do this with a model validation, and an index would help as well. Warning though, if you do the unique index without the accompanying ActiveRecord validation your saves will fail silently and cause a usability/debugging headache.

This should do it:

class Review < ActiveRecord::Base
  validates :user_id, :uniqueness => { :scope => :product_id,
    :message => "Users may only write one review per product." }
end

If you want to add the index, try this in a migration:

class AddUniquenessConstraintToReviews < ActiveRecord::Migration
  add_index  :review, [:user_id, :product_id],
    :name => "udx_reviews_on_user_and_product", :unique => true
end

Edit: As a full-time Rails dev I still refer to the ActiveRecord docs for refreshers on the syntax of these things pretty regularly. You should too!