Nested transaction for find_or_create_by! queries.

For background see
https://apidock.com/rails/v4.2.7/ActiveRecord/Relation/find_or_create_by.

app/models/user_interacted_project.rb

@@ -23,14 +23,20 @@ class UserInteractedProject < ActiveRecord::Base
       }
 
       cached_exists?(attributes) do
+        transaction(requires_new: true) do
           begin
-          find_or_create_by!(attributes)
+            where(attributes).select(1).first || create!(attributes)
             true # not caching the whole record here for now
           rescue ActiveRecord::RecordNotUnique
+            # Note, above queries are not atomic and prone
+            # to race conditions (similar like #find_or_create!).
+            # We retry and make sure the outer transaction (if any)
+            # is not aborted because of this.
             retry
           end
         end
       end
+    end
 
     # Check if we can safely call .track (table exists)
     def available?