Prevent Facebook count updates to non-canonical locations

app/models/concerns/wakes/metrics/facebook.rb

@@ -8,7 +8,7 @@ module Facebook
       included do
         store_accessor :document, :facebook_count, :facebook_count_updated_at
 
-        before_validation :prevent_decreasing_update, on: :update
+        before_validation :prevent_update_of_legacy_location, :prevent_decreasing_update, on: :update
 
         def enqueue_facebook_count_update
           Wakes::UpdateFacebookMetricsJob.perform_later(self)
@@ -24,6 +24,14 @@ def update_facebook_count(new_facebook_count)
 
         protected
 
+        def prevent_update_of_legacy_location
+          if facebook_count_will_change? && !canonical
+            Rails.logger.error "Received a request to update facebook metrics for non-canonical location #{path}, " \
+                              "from #{old_count} to #{new_count}. Ignoring it!"
+            throw :abort
+          end
+        end
+
         def prevent_decreasing_update
           if new_count < old_count
             Rails.logger.error "Received a request to update facebook metrics for location #{path}, " \
@@ -39,6 +47,11 @@ def old_count
         def new_count
           changes[:document]&.second.try(:[], :facebook_count).to_i
         end
+
+        # from https://github.com/rails/rails/issues/16808#issuecomment-112264052
+        def facebook_count_will_change?
+          changes[:document] && changes[:document].map { |v| v.try(:[], :facebook_count) }.uniq.length > 1
+        end
       end
     end
   end

app/services/wakes/facebook_count_updater_service.rb

@@ -4,7 +4,7 @@ class Wakes::FacebookCountUpdaterService
   attr_reader :locations, :wrapper
 
   def initialize(*locations)
-    @locations = locations.flatten
+    @locations = locations.flatten.select(&:canonical)
     @wrapper = Wakes::FacebookMetricsWrapper
   end
 

spec/services/wakes/facebook_count_updater_service_spec.rb

@@ -68,6 +68,8 @@
     let!(:location_1) { create(:location, :facebook_count => 4) }
     let!(:location_2) { create(:location, :facebook_count => 10) }
     let!(:location_3) { create(:location, :facebook_count => 12) }
+    let!(:legacy_location_1) { create(:location, :non_canonical, :facebook_count => 3) }
+    let!(:legacy_location_2) { create(:location, :non_canonical, :facebook_count => 6) }
 
     subject { described_class.new([location_1, location_2, location_3]) }
 
@@ -78,28 +80,34 @@
           .to receive(:new).and_return(facebook_wrapper)
         allow(facebook_wrapper).to receive(:share_counts).and_return(location_1.url => 20,
                                                                      location_2.url => 30,
-                                                                     location_3.url => 40)
+                                                                     location_3.url => 40,
+                                                                     legacy_location_1.url => 50,
+                                                                     legacy_location_2.url => 60)
       end
 
       before do
-        location_1.resource.locations << create(:location, :non_canonical, :facebook_count => 3)
-        location_2.resource.locations << create(:location, :non_canonical, :facebook_count => 6)
+        location_1.resource.locations << legacy_location_1
+        location_2.resource.locations << legacy_location_2
       end
 
-      it 'updates the facebook count of all the locations' do
+      it 'updates the facebook count of all canonical locations' do
         subject.update_facebook_count
         expect(location_1.facebook_count).to eq(20)
         expect(location_2.facebook_count).to eq(30)
         expect(location_3.facebook_count).to eq(40)
+        expect(legacy_location_1.facebook_count).to eq(3) # original value
+        expect(legacy_location_2.facebook_count).to eq(6) # original value
       end
 
-      it 'updates the facebook_count_updated_at for all locations' do
+      it 'updates the facebook_count_updated_at for all canonical locations' do
         time = Time.zone.now
         Timecop.freeze(time)
         subject.update_facebook_count
         expect(location_1.facebook_count_updated_at).to be_within(0.1).of(time)
         expect(location_2.facebook_count_updated_at).to be_within(0.1).of(time)
         expect(location_3.facebook_count_updated_at).to be_within(0.1).of(time)
+        expect(legacy_location_1.facebook_count_updated_at).not_to be_within(0.1).of(time)
+        expect(legacy_location_2.facebook_count_updated_at).not_to be_within(0.1).of(time)
       end
 
       it 'aggregates the facebook counts of associated resource' do