Discard nil Hash values in Ruby

Sometime we need to cleanup a hash based for nil values. If you're using Rails/ActiveSupport it's really easy.

Live preview Rails Mailer templates while developing

Developing email templates and sending a new mail every time to view a change is very inefficient and painful. Rails comes in rescue again. With mailer preview, you can view the changes in your browser just like any other page template.

How to change table for Rails models on the fly

Maybe you need your multi tenant application database to partition horizontally (shard). Probably you want to store different customers data in different tables.