Ruby Rails 3.2 How to group_by by an hash of array of attributes?

Question

I have a model Defect with attribute found_in. I have a hash test_phases whose keys are various test phases and whose value is an array of found_in values. Is there a way to group the Defect by test_phases? something like Defect.group_by(?test_phases)?.

The code I'm using is ugly

defects = {}
test_phases.each do |test_phase, found_ins|
  defects[test_phase] ||= Defect.where(found_in: found_ins].all
end

Answer 1

You don't need to group, since you are iterating a hash (no duplicate keys), the output hash won't have multiple elements by key. Simply use map + Hash (or mash for Facets connoisseurs):

defects = Hash[test_phases.map do |test_phase, found_in_values|
  [test_phase, Defect.where(found_in: found_in_values)]
end]

Answer 2

I solved this by creating a TestPhase model with a join table DefectFound

test_phase.rb:
    has_many :defect_founds

defect_found.rb:
    belongs_to :test_phase

defect.rb:
    belongs_to :defect_found, foreign_key: :found_in, primary_key: :name # defect_found.name = defect.found_in
    has_one :test_phase, through: :defect_found

controller:
    @defects = Defect.includes(:test_phase).select('found_in, COUNT(id) as backlog').group(:found_in).group_by(&:test_phase)

view:
    %table
      - @defects.each do |test_phase, backlogs|
        %tr
          %td= test_phase.name if test_phase.present?
          %td= backlogs.map(&:backlog).inject(:+)