JPA Parent child relationship

https://vladmihalcea.com/the-best-way-to-map-a-onetomany-association-with-jpa-and-hibernate/


a quick reminder to myself:

if Post -> PostComment is a Unidirectional association (Post has a List<PostComments; but PostComment has no reference to Post),
then the insertion of each PostComment is done in two phases (INSERT + UPDATE who sets the parentId on the child table).
For this reason, the parentId column CANNOT BE DECLARED AS NOT NULL.

I don't like that.... ultimately that column should NEVER be null...

On the other hand, if you setup a full bidirectional relationship, only ONE insert is done, and you can keep parentId as NOT NULL.
To achieve that, you must explicitely set the Post attribute on the PostComment entity, before you persist/merge (I think, at least)