determine recipients and queue notifications _after_ transaction commit

fixes CNVS-22546

test plan:
  * regression test notifications

Change-Id: I7896f03b18b19003cff6228aefa72029a8c08a29
Reviewed-on: https://gerrit.instructure.com/61249
Reviewed-by: Joel Hough <joel@instructure.com>
Tested-by: Jenkins
QA-Review: Adrian Russell <arussell@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

gems/broadcast_policy/broadcast_policy.gemspec

@@ -16,6 +16,7 @@ Gem::Specification.new do |s|
   s.test_files = Dir["spec_canvas/**/*"]
 
   s.add_dependency "activesupport"
+  s.add_dependency "after_transaction_commit"
   s.add_development_dependency "rspec"
   s.add_development_dependency "pry"
 end

gems/broadcast_policy/lib/broadcast_policy/notification_policy.rb

@@ -40,21 +40,23 @@ module BroadcastPolicy
       notification = BroadcastPolicy.notification_finder.by_name(self.dispatch)
       return if notification.nil?
 
-      to_list = record.instance_eval(&self.to)
-      to_list = Array(to_list).flatten
-      return if to_list.empty?
+      record.connection.after_transaction_commit do
+        to_list = record.instance_eval(&self.to)
+        to_list = Array(to_list).flatten
+        next if to_list.empty?
 
-      asset_context = record.instance_eval(&self.context) if self.context
-      data = record.instance_eval(&self.data) if self.data
+        asset_context = record.instance_eval(&self.context) if self.context
+        data = record.instance_eval(&self.data) if self.data
 
-      BroadcastPolicy.notifier.send_notification(
-        record,
-        self.dispatch,
-        notification,
-        to_list,
-        asset_context,
-        data
-      )
+        BroadcastPolicy.notifier.send_notification(
+          record,
+          self.dispatch,
+          notification,
+          to_list,
+          asset_context,
+          data
+        )
+      end
     end
 
   end

gems/broadcast_policy/spec/broadcast_policy/notification_policy_spec.rb

@@ -10,6 +10,7 @@ describe BroadcastPolicy::NotificationPolicy do
   end
 
   let(:test_notification) { double(:test_notification) }
+  let(:test_connection_class) { Class.new { def after_transaction_commit; yield; end } }
 
   before(:each) do
     BroadcastPolicy.notifier = MockNotifier.new
@@ -17,7 +18,7 @@ describe BroadcastPolicy::NotificationPolicy do
   end
 
   it "should call the notifier" do
-    record = double('test record', skip_broadcasts: false)
+    record = double('test record', skip_broadcasts: false, connection: test_connection_class.new)
     subject.broadcast(record)
     expect(BroadcastPolicy.notifier.messages.count).to eq(1)
   end
@@ -36,21 +37,21 @@ describe BroadcastPolicy::NotificationPolicy do
   end
 
   it "should not send if there is not a recipient list" do
-    record = double('test object', skip_broadcasts: false)
+    record = double('test object', skip_broadcasts: false, connection: test_connection_class.new)
     subject.to = ->(_) { nil }
     subject.broadcast(record)
     expect(BroadcastPolicy.notifier.messages).to be_empty
   end
 
   it "should send even if there isn't a context" do
-    record = double('test object', skip_broadcasts: false)
+    record = double('test object', skip_broadcasts: false, connection: test_connection_class.new)
     subject.context = ->(_) { nil }
     subject.broadcast(record)
     expect(BroadcastPolicy.notifier.messages).to_not be_empty
   end
 
   it "should send even if there isn't data" do
-    record = double('test object', skip_broadcasts: false)
+    record = double('test object', skip_broadcasts: false, connection: test_connection_class.new)
     subject.data = ->(_) { nil }
     subject.broadcast(record)
     expect(BroadcastPolicy.notifier.messages).to_not be_empty