Specifically, I want to focus on the One-to-Many relationship in Hibernate and how we go about mapping it out in our Java objects.
But before we do, a word on unidirectional and bidirectional relationships.
They are automatically persisted when referenced by a persistent object and are automatically deleted when unreferenced.
So if you wana give an user the same role read it from the database first. You probably will create valid user roles before creating an user or update it afterwards.In Hibernate, it’s possible to map all three relationships that are available in a standard database, these include: But what Hibernate also includes is the ability to make EACH of those relationships either unidirectional or bidirectional.This means that we can have a unidirectional One-to-One and a bidirectional One-to-One mapping, as well as a unidirectional One-to-Many and a bidirectional One-to-Many, as well as a unidirectional Many-to-Many and a bidirectional Many-to-Many relationship. So what exactly are unidirectional and bidirectional relationships? Let’s say for example that we have a One-to-Many relationship between as well as the appropriate getters and setters.You'll therefore need to do this: Either, change the unidirectional @Many To One relationship to a bi-directional @Many To One, or a unidirectional @One To Many.You can then cascade REMOVE operations so that Entity Manager.remove will remove the parent and the children.This is the key to mapping out a unidirectional relationship.