Rails loop refactor

Question

I have created a loop, to calculate a total rating of a record. To do this I am first looping through all the child records (ratings), extracting the rating from each row, adding it to the total and then outputting the total.

<% total = 0 %>
<% for ratings in @post.ratings %>
    <% total = (total + ratings.rating) %>
<% end %>
<%= total %>

My question is, simply, Is this the rails way?

It achieves the desired result, although needs 5 lines to do so. I am worried I am bring old habits from other languages into my rails project, and I am hoping someone could clarify if there is an easier way.

Jeff Doyle · Accepted Answer · 2013-02-17 07:05:55Z

3

The following, preferably in the controller, will do it succinctly:

@rating = @post.ratings.sum { &:rating }

If that seems cryptic, you might prefer

@rating = @post.ratings.inject(0) { |sum, p| sum + p.rating }

Note, however, that this will fail if any of the ratings are null, so you might want:

@rating = @post.ratings.inject(0) { |sum, p| sum + (p.rating || 0) }

answered Feb 17, 2013 at 7:05

Jeff Doyle

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1 Comment

Aleksei Chernenkov Over a year ago

You can convert rating to_i explicitly to avoid || operator. But anyway - the first example is the only one you should accept - it reduces count of db queries to 1 and increase performance.

Oleksi · Accepted Answer · 2013-02-17 06:30:41Z

1

You should generally keep logic out of your views. I would put that code in a helper or a controller, and the call a method to calculate the total

answered Feb 17, 2013 at 6:30

Oleksi

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Comments

mind.blank · Accepted Answer · 2013-02-17 06:44:47Z

0

Put the following in your controller, then you just need to use @rating in your view:

total = 0
@rating = @post.ratings.each { |r| total += r.rating }

Or you could move it into the Post model and do something like:

def self.total_rating
  total = 0
  ratings.each { |r| total += r.rating }
  total
end

and then simply call @post.total_rating

answered Feb 17, 2013 at 6:44

mind.blank

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