I have some XML of the following structure to import into Drupal:
<list> <item id="0001" xml="http://www.example.com/0001.xml" dateChanged="24 June 2013 12:00:00"></item> <item id="0002" xml="http://www.example.com/0002.xml" dateChanged="24 June 2013 12:56:00"></item> ... </list>
I have set up Migrate to run with cron every minute: read through the list, grab each item's XML and indiscriminately update the destination node. My Migrate source only uses the data from these linked documents, nothing from the list. But this is overkill. What I would like to do is to check the dateChanged dates, compare it to the corresponding last modified date in the node table, and only update the nodes that need it (if the corresponding XML doc has been updated). Can I do this with the last modified field as a highwater field?