Here are a few quick tips for a Drupal 7 to Drupal 8 migration. I will add more over time; admittedly it’s pretty lame right now!
For general Drupal 8 Migrate API tips, you may also want to check out my other post: Drupal 8 Migrate – Tips and Tricks
If you’re using a source plugin like d7_user or d7_node it will help you understand what’s happening if you view the source code for the plugin. Pay close attention to the query(), prepareRow(), and fields() methods.
I’m not going into much detail here but hopefully this helps someone.
If you need to migrate only published nodes you can extend the d7_node plugin and add a condition to the query.
First, create a file in your module like /modules/custom/mysite_migrate/src/Plugin/migrate/source/MysiteNewsNode.php that extends the d7_node plugin: