title: "postgresql gem is not loaded" error deploying a Ruby on Rails application on Heroku
body: <p>I am trying to use <strong>postgresql</strong> with <strong>Ruby on Rails</strong> on <strong>Heroku</strong> but got an error </p>
  
  <pre><code>Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord). (Gem::LoadError)
  </code></pre>
  
  <p>Please help me to solve this issue.</p>