01 January 2017

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

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Anee Syed
Drupal Developer

We 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.#Rails

This should do it:

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

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

the ActiveRecord docs for refreshers on the syntax of these things pretty regularly. You should too!

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