declare a variable ruby on rails

Question

In the example given at

http://guides.rubyonrails.org/getting_started.html

I got confused by variable "comment".

The original version is

<h2>Comments</h2>
<% @post.comments.each do |comment| %>
  <p>
    <strong>Commenter:</strong>
    <%= comment.commenter %>
  </p>

  <p>
    <strong>Comment:</strong>
    <%= comment.body %>
  </p>
<% end %>

In this version, I can understand "comment" is from |comment|

Then, in section 7, this part is changed into

<h2>Comments</h2>
<%= render @post.comments %>

In the app/views/comments/_comment.html.erb the code is

<p>
  <strong>Commenter:</strong>
  <%= comment.commenter %>
</p>

<p>
  <strong>Comment:</strong>
  <%= comment.body %>
</p>

Then I got confused. Where is "comment" declared?

Is there a tutorial introducing how variables declared in ruby on rails?

Thank you very much.

Amadan · Accepted Answer · 2014-03-20 04:26:53Z

3

This article should clear it up. The core of it is that

<% render @post.comments %>

will do the same thing as

<% @post.comments.each do |comment| %>
  <%= render partial: 'comments/comment', locals: { comment: comment } %>
<% end %>

Your variable comment inside the partial template is declared by render, triggered by the locals hash. The article further explains the magic of how you get the latter from the former.

answered Mar 20, 2014 at 4:26

Amadan

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9 Comments

user3440433 Over a year ago

Thanks. The place I feel very confusing is where "comment" is. We have "comments". But I don't get the rule from "comments" to "comment".

user3440433 Over a year ago

If I have <% render @post.abcs %>, should I always expect "do |abc|" ?

user3440433 Over a year ago

By the way, could you please let me know the link of explanation of this magic? I can't find it?

rubyprince Over a year ago

@user3440433, robots.thoughtbot.com/rendering-collections-in-rails is the link, are you not getting it?

Amadan Over a year ago

Yes, render @post.abcs would define an abc local in your partial template.

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