title: How would you have an object observe/subscribe to itself to watch a certain field?
body: <p>In my observer I'm trying to write a method for a product to "look at itself" and then find the same product with the <code>:price</code> field being the only difference. In other words, I'm trying to notify a user if they subscribe to product of lower prices.</p>
  
  <p>Here is my Products table:</p>
  
  <pre><code>create_table :products do |t|
    t.string  :name
    t.decimal :price
    t.integer :user_id
    t.integer :store_id
    t.boolean :watch_price
  end
  </code></pre>
  
  <p>And then I have my observer for it:</p>
  
  <pre><code>class ProductObserver &lt; ActiveRecord::Observer
    def after_update(product)
      if product.watch_price
  
      end
    end
  end
  </code></pre>
  
  <p>So if the boolean <code>:watch_price</code> is true then a user has subscribed to that product. I put it in the <code>after_update(product)</code> because I want the users to be able to select the <code>watch_price</code> checkbox and then it does a Cron job instantly and then every hour after that on the database. </p>
  
  <p>The issue I'm having is making a Product evaluate itself and search for Products that are just the same with the only difference being the <code>:price</code> field. How would this be done?</p>
  
  <p>Thanks in advance, a newbie could use some help!</p>