The Rails presence Method

Note: This article was originally written at https://blog.edwardloveall.com/rails-presence-method

Rails has a convenient method that I discovered the other day: presence. All it does is return itself if present?. It's a pretty simple method:

def presence
  self if present?
end

The documentation has a great example that simplifies this:

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

to this:

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

Here's another use case. Imagine your app has a page where you can search for users. There's a show.html.erb template, and two partials: user.html.erb and no_results.html.erb.

Your controller will search for users and assign them to an instance variable. If no users were found, we'd rather show the no_results partial instead of a blank page:

<% if @users.present? %>
  <%= render @users %>
<% else %>
  <% render 'no_results' %>
<% end %>

With presence we can make this code shorter but still readable.

<%= render @users.presence || 'no_results' %>

Most of the time present? is probably what you're looking for, but sometimes presence really cleans up your code. Keep it in mind.