I realize the contract for set says that contained objects must be unique. What do you do when you want to support cascaded inserts when the children are in a set? I ended up overriding equals and getHashCode to id if one exists otherwise I used a candidate key's attributes. What do you do when you don't have a candidate key -- look at all attributes? Use a list?

If the app does not know about the existence of the child it needs to get it by it's functional uniqueness before any add.
I manage that in the business process layer