What does "render @collection" do?

Question

I'm trying to learn Rails better by looking at example applications, and while looking at this line of the source of railscasts.com, I noticed it does this:

<div class="episodes">
    <%= render @episodes %>
  </div>

What exactly is going on here? Why isn't this documented on the render function? Or is it?

Answer 1

This is a handy shortcut for doing

<%= render :partial => "episode", :collection => @episodes %>

which is another way of doing

<% for episode in @episodes do %>
  <%= render :partial => "episode", :locals => { :episode => episode }
<% end %>

which is pretty obvious in what it does :)

Hope that makes sense :)

btw it's really surprising I couldn't find the docs for this too.

Answer 2

This is a new shortcut:

<%= render @episodes %>

# equivalent to
<%= render :partial => 'episode', :collection => @episodes %>

You can also do shortcuts with single items

<%= render 'comment', comment => @comment  %>

# equivalent to
<%= render :partial => 'comment', :locals => {:comment => @comment} %>

Answer 3

This is shorthand for

render :partial => "episode", :collection => @episodes

The form above is documented in the Rails API docs under render (ActionController::Base). The shorthand form is not documented as far as I can see except in the Rails Guides.