use single query to invalidate cache for all affected work packages

db/migrate/20190722082648_add_derived_estimated_hours_to_work_packages.rb

@@ -45,7 +45,7 @@ class AddDerivedEstimatedHoursToWorkPackages < ActiveRecord::Migration[5.2]
     create_customizable_journals last_id: last_id
     create_attachable_journals last_id: last_id
 
-    work_packages.each(&:touch) # invalidate cache
+    touch_work_packages work_packages # to invalidate cache
   end
 
   ##
@@ -164,4 +164,12 @@ class AddDerivedEstimatedHoursToWorkPackages < ActiveRecord::Migration[5.2]
       WHERE #{journals}.id > #{last_id} -- make sure to only create entries for the newly created journals
     ")
   end
+
+  def touch_work_packages(work_packages)
+    where = work_packages.arel.where_sql
+
+    WorkPackage.connection.execute("
+      UPDATE work_packages SET updated_at = NOW(), lock_version = lock_version + 1 #{where}
+    ")
+  end
 end