Hibernate JPA双向一对多结果与约束冲突异常

Question

我开始学习hibernate JPA，并尝试创建双向一对多关系，但由于某种原因，它导致了org.hibernate.exception.ConstraintViolationException: could not execute statement

假设我有一个实体卡和实体甲板。每个牌组可以有多张牌，但每张牌只能属于一个牌组。我是这样做的：

这是卡片实体：

/**
* 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;
}

这是甲板：

/**
* 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<>();
}

现在这是我的存储库，我想在这里持久化卡实体：

...
/**
* @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;
}
}
...

在执行entityManager.flush()时，由于违反了约束而崩溃。我无法想象为什么。

Answer 1

因为Card#deck引用的Deck是非托管的和/或它的id不存在。如果要将Deck与卡一起保存，则需要在Card#deck上配置PERSIST级联。