Question

I’m using Rails 3.0 and the acts_as_taggable_on gem. I have a Candy model and candies can have multiple tags for flavors. Let’s say

Candy1.tags #['apple', 'orange']
Candy2.tags #['orange', 'banana']
Candy3.tags #['apple', 'kiwi']

I want a list of tags with associated candies below them, like so:

Apple

• Candy1
• Candy3

Orange

• Candy1
• Candy2

…etc.

I’ve tried

Candy.all.group_by{ |candy| candy.tags }

but that treats the array of tags as a single entity, returning something like this:

[‘apple’, ‘orange’]

• Candy1

[‘orange’, ‘banana’]

• Candy2

Lacking a group_by_each method, whats the best way to accomplish this? Another Stack Overflow question explains how to do this in memory with simple hashes, but I wonder if there’s a more database-oriented way to do it with ActiveRecord associations.

Answer 1

You can iterate over the candies and store them on a hash base on the tag:

grouped = {}
Candy.all.each do |candy|
  candy.tags.each do |tag|
    grouped[tag] ||= []
    grouped[tag] << candy
  end
end

At the end you will get:

{'apple' => [candy1, candy2], 'orange' => [] ...}

Hope this helps you