Because the `Delete Rule` is Nullify. Only way to nullify the relationship is to be optional. Otherwise, choose Cascade/Delete. There's also not really a way to represent that the relationship does NOT exist.
– BrandonDec 31 '16 at 04:39
`Cascade Delete the objects at the destination of the relationship when you delete the source.` I have a to-many relationship here, and I set cascade delete in the **parent** entity not in child.
– JánosDec 31 '16 at 04:44