Hibernate如何在OneToMany关系中将null设置为外键列

Question

I have 2 classes: User and Company.

User
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "company_id")
public Company getCompany() {
    return company;
}

Company
@OneToMany(mappedBy = "company", fetch = FetchType.LAZY)
public List<User> getEmployees() {
        return employees;
}

I need when I delete Company to set foreign key company_id as null in User table. How could I do this?

Answer 1

Typically the relationship you describe would be created with a constraint on the Foreign Key that references the User entity. This is so you can't set it to null . If you set it to null, it becomes an orphaned row, which makes for a bad database.

If, on the other hand, you need the two entities to persist separately from their joins, then your relationship is not as you are describing it.

It seems that in this case Companies and Users (Persons?) both need to exist without necessarily being joined. I would suggest a new entity, something like Employment . It would effectively act as a join table in the sense that it has both Company and User id's, but it could also have more information such as startdate , enddate , and current employer .