Checking Presence in Rails

Written on February 10, 2016 Updated on July 23, 2018: Added new section "Upgrade Your Conditionals"

Instead of using .empty? or .blank?, Rails provides us with a great method called .presence. This method:

Returns the receiver if it’s present otherwise returns nil. object.presence is equivalent to.

This is great to use to clean up ternaries. Let’s say you had something like this:

foo = bar.name.empty? ? "No name" || bar.name

Using .presence we can rewrite this:

foo = bar.name.presence || "No name"

While it’s only a few characters shorter, it reads so much better.

The Rails docs has a good example:

state   = params[:state]   if params[:state].present?
country = params[:country] if params[:country].present?
region  = state || country || 'US'

Becomes:

region = params[:state].presence || params[:country].presence || 'US'

So give it a go! See where you can save a few characters and improve readability in your code base.

Upgrade Your Conditionals

Another great example is using it in an assignment conditional. I use the following for building this site:

<% if tldr = current_page.data.tldr.presence %>
  <div class="article-tldr">
    <h4 title="Too Long, Didn't Read">tl;dr</h4>
    <%= Tilt::RedcarpetTemplate.new { tldr }.render %>
  </div>
<% end %>

If current_page.data.tldr.presence returns nil the content is not rendered. If it has content it will be assigned to tldr and we can use that later inside the block.