The @ManyToOne associations are optional by default, so you don’t need to set anything if you want them to be nullable. However, because you set the optional=false attribute, you made it mandatory. So instead of: @ManyToOne(optional = false, fetch = FetchType.LAZY) Set it like this: @ManyToOne(fetch = FetchType.LAZY) The optional is true by default. On … Read more
They look exactly the same on schema but there is difference on Hibernate Layer. If you try something like that: Address address = new Address(); Order order1 = new Order(); order1.setAddress(address); Order order2 = new Order(); order2.setAddress(address); save(); Everything will be OK. But, after save if you try get Order: @OneToOne case: org.hibernate.HibernateException: More than … Read more
I am not really sure about your question (the meaning of “empty table” etc, or how mappedBy and JoinColumn were not working). I think you were trying to do a bi-directional relationships. First, you need to decide which side “owns” the relationship. Hibernate is going to setup the relationship base on that side. For example, … Read more
As an answer to okutane, please see snippet: @JoinColumn(name = “car_id”, insertable = false, updatable = false) @ManyToOne(targetEntity = Car.class, fetch = FetchType.EAGER) private Car car; @Column(name = “car_id”) private Long carId; So what happens here is that when you want to do an insert/update, you only populate the carId field and perform the insert/update. … Read more
https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/annotations-reference.html#annref_joincolumn Add nullable = false to the JoinColumn annotation: @ORM\JoinColumn(…, nullable=false)
Suppose you have an Order and an OrderLine. You can choose to have a unidirectional OneToMany between Order and OrderLine (Order would have a collection of OrderLines). Or you can choose to have a ManyToOne association between OrderLine and Order (OrderLine would have a reference to its Order). Or you can choose to have both, … Read more
If you are using hibernate as your JPA provider you can use the annotation @OnDelete. This annotation will add to the relation the trigger ON DELETE CASCADE, which delegates the deletion of the children to the database. Example: public class Parent { @Id private long id; } public class Child { @Id private long id; … Read more
Yes, it a vice versa. It depends on which side of the relationship the entity is present on. For example, if one department can employ for several employees then, department to employee is a one to many relationship (1 department employs many employees), while employee to department relationship is many to one (many employees work … Read more
The meaning of CascadeType.ALL is that the persistence will propagate (cascade) all EntityManager operations (PERSIST, REMOVE, REFRESH, MERGE, DETACH) to the relating entities. It seems in your case to be a bad idea, as removing an Address would lead to removing the related User. As a user can have multiple addresses, the other addresses would … Read more