Dealing with nil in views (ie nil author in @post.author.name)

Question

I want to show a post author's name; <% @post.author.name %> works unless author is nil. So I either use unless @post.author.nil? or add a author_name method that checks for nil as in <% @post.author_name %>. The latter I try to avoid.

The problem is that I may need to add/remove words depending on whether there is a value or not. For instance, "Posted on 1/2/3 by " would be the content if I simply display nil. I need to remove the " by " if author is nil.

Answer 1

You can use try:

<%= @post.author.try(:name) %>

It will attempt to call the name method on @post.author if it is non-nil. Otherwise it will return nil, and no exception will be raised.

---

Answer to your second question: In principle there is nothing wrong with the following:

<% if @post.author %>
  written by <%= @post.author.name %>
<% end %>

or

<%= "written by #{@post.author.name}" if @post.author %>

But if this is a recurring pattern, you might want to write a helper method for it.

# app/helpers/authors_helper.rb or app/helpers/people_helper.rb
class AuthorsHelper
  def written_by(author)
    "written by #{author.name}" if author
  end
end

# in your views
<%= written_by(@post.author) %>

Answer 2

Write a method which accepts any variable and checks to see if it is nuil first, and if it is not displays it. Then you only have to write one method.

Answer 3

Null object pattern is one way to avoid this. In your class:

def author
  super || build_author
end

This way you will get an empty author no matter what. However, since you don't actually want to have an empty object sometimes when you do expect nil, you can use presenter of some kind.

class PostPresenter
  def initialize(post)
    @post = post
  end

  def post_author
    (@post.author && @post.author.name) || 'Anonymous'
  end
end

Another way is using try, as in @post.author.try(:name), if you can get used to that.

Answer 4

I found your question interesting as I have often come across similar situations, so I thought I'd try out making my first Rails plugin.

I'm afraid I haven't put in any tests yet but you can try it out http://github.com/reubenmallaby/acts_as_nothing (I'm using Ruby 1.9.1 so let me know if you get any problems in the comments or on Github!)