Add method to get all teams within a stage

app/models/stage.rb

@@ -4,4 +4,8 @@ class Stage < ApplicationRecord
   belongs_to :tournament
   has_many :matches, dependent: :destroy
   has_many :groups, dependent: :destroy
+
+  def teams
+    groups.map{|g| g.matches.map{ |m| m.match_scores.map{ |ms| ms.team}}}.flatten.uniq
+  end
 end