映射到子表两次 - @OneToMany和@ManyToOne

Question

I'm trying to model a parent entity which has a collection of child entities (childHistory) and also a pointer to the last added child (currentChild)

class Parent {
    //unidirectional
    @OneToOne(cascade = CascadeType.PERSIST, optional = false)
    @JoinColumn(name = "current_child_id")
    private Child currentChild;

    //bidirectional
    @OneToMany(mappedBy = "parent")
    private List<Child> childHistory;

    public Parent() {
        currentChild = new Child(this);
        childHistory = new ArrayList<>();
        childHistory.add(currentChild);
    }

    public void add() {
        currentChild = new Child(this);
        childHistory = new ArrayList<>();
        childHistory.add(currentChild);
    }
}

class Child {
    @ManyToOne(optional = false)
    @JoinColumn(name = "parent_id")
    private Parent parent;
    public Child(Parrent parent) {
        this.parent = parent;
    }
}

I currently get an exception for transient entities when I try to save the Parent (and count on cascading to persist the children). I can't save the Parent beforehand since I init everything in the Parent ctor.

Warnings (that lead to exceptions...):

WARN: HHH000437: Attempting to save one or more entities that have a non-nullable association with an unsaved transient entity. The unsaved transient entity must be saved in an operation prior to saving these dependent entities. Unsaved transient entity: ([com.Parent#<null>]) Dependent entities: ([[com.Child#<null>]]) Non-nullable association(s): ([com.Child.entity])

---

WARN: HHH000437: Attempting to save one or more entities that have a non-nullable association with an unsaved transient entity. The unsaved transient entity must be saved in an operation prior to saving these dependent entities. Unsaved transient entity: ([com.Child#<null>]) Dependent entities: ([[com.Parent#<null>]]) Non-nullable association(s): ([com.Parent.currentChild])

Is there a way to model this correctly and have NOT NULL db column with hibernate.

EDIT: For a repro see this gist: https://gist.github.com/jlogar/2da2237640aa013f2cfbda33a4a5dc84

Answer 1

The exception is refering to saving transient entity, this means you are trying to save entity which has relation with a non managed entity, since your parent is cascading the onetoone child then the problem would be with childHistory, since this is a bidirectional relation it would make since to cascade the children also

@OneToMany(mappedBy = "parent",cascade=CascadeType.PERSIST)
private List<Child> childHistory;