JPA @OneToMany with 1 - 1..* relationship

askstackoverflow :

How to properly map @OneToMany relationship where to create entity, on @One side of @OneToMany relationship, it is required to have atleast one entity from @Many side but entity on @Many side also requires entity on @One side to exist? To put this nightmare of a sentence simply, this is the scenario I have:

This is what I want:

[ENTITY A] 1 <-----> (1..*)[ENTITY B]

At the moment I have this:

[ENTITY A] 1 <-----> (0..*)[ENTITY B]

Which is easily done like this.

@OneToMany(cascade=CascadeType.ALL, mappedBy="customer")
public Set<Agreement> agreements = new HashSet<>();

and

@ManyToOne
@JoinColumn(name = "CUSTOMER_ID", nullable=false)
private Customer customer;

So the problem is my CUSTOMER table has no column corresponding to AGREEMENT table therefore I can't enforce rule of creating Customer only when Agreement is given. At the moment I can only setup rule to create Agreement when Customer is given because AGREEMENT table has column corresponding to CUSTOMER tabel, which is easily done by nullable=false condition.

pdem :

JPA doesn't provide a way to validate this, but Hibernate Validator does:

@NotNull
@Size(min=1)
public Set<Agreement> agreements = new HashSet<>();

Then you have to manually test it via the Validator:

ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
Validator validator = validatorFactory.getValidator();
validator.validate(customer)