Ruby on Rails magic: first impression


Being a PHP developer for more than 5 years I recently started learning Ruby on Rails. While I'm used to "Convention over Configuration" principles in PHP frameworks I found not a few conventions in Ruby on Rails that amazed me in some way.

There is something that amazed me more than anything else and I couldn't help myself from writing about it when I discovered it in this book written by Michael Hartl.

#Render a partial for model objects

Assuming we have a simple Controller action:

def index
  @users = User.all

..and a simple partial template called _user.html.erb:

<p><%= %></p>

..let's take a look at it's View (index.html.erb):

<% @users.each do |u| %>
  <%= render 'user', user: u %>
<% end %>

Here, a partial _user.html.erb that resides in the same directory as current template file is being rendered for every @users element. Pretty straight-forward. Similarly I would do it in any PHP framework.

However as it turns out View's code can be replaced with just one line:

<%= render @users %>

It looks simple and logical at first sight, however, if you think about it, there are so many things happening in this line.

Let's break it into pieces:

  • Rails infers that @users is a list of User objects.
  • Because @users is a list Rails iterates through every element.
  • Because @users consists of User objects it assigns every object to partial's variable user and renders a partial called _user.html.erb

If @users would be a list of Post objects, Rails would set partial's variable called post and render a partial called _post.html.erb for every list element.


I'm a big fan of convention over configuration paradigm and such examples excite me every time I discover them. I know it slows down the learning progress in the beginning but it saves time in the long run.

Hi, I'm Sergey, 30yo, father of 2, currently based in Tel Aviv, Israel.

I'm mostly passionate about #music, #programming, #sport, #ui, #ux alphabetical order :)

Read more about me in my Résumé