Tip: This course is built on Symfony 3, but most of the concepts apply just fine to Symfony 4.
With the basic of Doctrine relations behind us, it's time to dive deeper and get our hands dirty with some real-world, but complex collections. Honestly, this is the hardest part of Doctrine: so let's get it right:
orphanRemovalto delete items in a collection
cascadeto save items in a collection
Doctrine relationships take a little bit more work to get setup. So let's master this stuff, setup our relationships to win, and get back to work.