Iterating through an lazy load array - ruby-on-rails

Question

I'm tryin to build an array of hashes and then iterate through.
If I use the code below
#elements = [{:profile_id=>"123"}, {:profile_id=>"456"}]
#categories = Array.new
#elements.each do |element|
category = Category.find_by_profile_id(element[:profile_id])
#categories.push(category)
end
It will find the last object and it will add to the array. However I would like to fetch all the records with that id.
I have been trying the code bellow
#elements = [{:profile_id=>"123"}, {:profile_id=>"456"}]
#categories = Array.new
#elements.each do |element|
category = RootCategory.where(profile_id: element[:profile_id])
#categories.push(category)
end
#response
[#<ActiveRecord::Relation [#<Category id: "123", ...">, #<Category id: "123", ..."> #<ActiveRecord::Relation [#<Category id: "456", ...">, #<Category id: "456", ...">]>]
I can't iterate through the returned array. If I try
#categories.each do |t|
puts t.name
end
#Prints
#Category
#Category

Answer 1

This is mostly because you are abusing each for mapping. ActiveRecord::Base#where returns a Relation object (without a loss of generality it might be considered an array here). What you need is Enumerable#flat_map:
elements = [{:profile_id=>"123"}, {:profile_id=>"456"}]
#categories =
elements.flat_map do |element|
RootCategory.where(profile_id: element[:profile_id])
end
or, even better, avoid multiple queries, since where happily accepts an array:
#categories =
RootCategory.where(profile_id: elements.map { |e| e[:profile_id] })
The latter is basically executing:
RootCategory.where(profile_id: [123, 456])
retrieving categories for all the profiles specified.