Hibernate JPA 雙向一對多結果與約束違反異常

Question

我開始學習 hibernate JPA 並嘗試創建雙向一對多關系，但由於某種原因，它會導致org.hibernate.exception.ConstraintViolationException: could not execute statement

假設我有一個實體卡和實體甲板。 每副牌可以有多張牌，但每張牌只能屬於一副牌。 我是這樣做的：

這是卡實體：

/**
 * Represents a card in deck.
 *
 * @author wintermute
 */
@Data
@Entity(name = "card")
@Table(name = "card")
@NamedQueries( {@NamedQuery(name = "Card.getAll", query = "SELECT c FROM card c WHERE c.containedInDeck = :deck_id"),
                @NamedQuery(name = "Card.remove", query = "DELETE FROM card c WHERE c.id = :id")})
public class Card
{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String containedText;

    @ManyToOne
    @JoinColumn(name = "deck_id")
    private Deck containedInDeck;
}

這是甲板：

/**
 * Represents card deck containing cards sorted by deck's type.
 *
 * @author wintermute
 */
@Data
@Entity
@Table(name = "deck")
public class Deck
{
    @Id
    @GeneratedValue
    private long id;
    @Column(name = "type")
    private String typeOfDeck;

    @OneToMany(mappedBy = "containedInDeck")
    @ElementCollection(targetClass = Card.class)
    private Set<Card> containedCards = new HashSet<>();
}

現在這是我要保存卡實體的存儲庫：

    ...
    /**
     * @param card to persist in database.
     * @return true if operation was successful, false if operation failed.
     */
    public long add(Card card)
    {
        try
        {
            entityManager.getTransaction().begin();
            entityManager.persist(card);
            entityManager.flush();
            entityManager.getTransaction().commit();
            return card.getId();
        } catch (IllegalStateException | PersistenceException e)
        {
            log.error("Could not save entity: " + card + ", message: " + e.getMessage());
            return -1L;
        }
    }
    ...

在執行entityManager.flush()時，由於違反約束而崩潰。 我無法想象為什么。

Answer 1

因為Card#deck引用的Deck是非托管的和/或它具有的 id 不存在。 如果要將Deck與卡一起保存，則需要在Card#deck上配置 PERSIST 級聯。