It's annoying to shut down and start up your Rails server when jumping between projects. Learn how to run multiple servers at the same time.
Rails 4.1 introduced the ability to preview email messages from your mailers without sending an email. Learn how ...
Rails' scopes don't work well with virtual attributes since they resolve to a SQL query. Instead you can throw them in an array and then sort by a virtual attribute.
How to maintain HMT behavior on a polymorphic association.
Sometimes metadata isn't available. Other times you don't want to rely on it. Here's a method for finding related content using term frequency / inverse document frequency.