The ActiveModel::Serializers gem can help you build JSON APIs through serializer objects. This provides a dedicated place to fully customize the JSON output. (10 minutes)

Learn how to easily add a user activity feed using the public_activity gem. Here I show both the default setup using model callbacks and a manual way to trigger activities. (10 minutes)

Allow users to import records into the database by uploading a CSV or Excel document. Here I show how to use Roo to parse these files and present a solution for validations. (10 minutes)

RubyGems can make it easy to add a feature to a Rails application, but it can also cause headaches down the road. Here I give some tips on researching gems to decide which one to choose, or when to do it from scratch. (7 minutes)

There are several gems to help implement tags in a Rails app. Here I show you how to integrate acts-as-taggable-on and then show how to do it from scratch. (11 minutes)

Bullet will notify you of database queries that can potentially be improved through eager loading or counter cache column. A variety of notification alerts are supported. (6 minutes)

Ransack allows you to easily build complex search forms. It also helps in adding sortable links and building a dynamic advanced search page. (10 minutes)

MiniProfiler allows you to see the speed of a request conveniently on the page. It also shows the SQL queries performed and allows you to profile a specific block of code. (9 minutes)

Sidekiq allows you to move jobs into the background for asynchronous processing. It uses threads instead of forks so it is much more efficient with memory compared to Resque. (10 minutes)

If you need to calculate an average user's rating or sum up a number of votes, consider using the activerecord-reputation-system gem. Here I will cover the basics and also briefly present a from-scratch solution. (10 minutes)