java - 抽象模式类型 'User_Book' 未知

Question

我有一个包含多个实体的数据库，特别是 Book 和 User。它们之间存在这样的 ManyToMany 关系:

书:

@Entity
@Table(name = "Books")
public class Book implements Serializable
{
  private static final long serialVersionUID = 1L;

  @Id
  @GeneratedValue(strategy = GenerationType.TABLE)
  @Column(name = "bookId", nullable = false, unique = true)
  private Long id;

  @Column(name = "title", nullable = false)
  private String title;

  @Column(name = "price", nullable = false)
  private int price;

  @ManyToMany(fetch = FetchType.EAGER)
  @JoinTable(name = "User_Book",
             joinColumns = @JoinColumn(name = "bookId"),
             inverseJoinColumns = @JoinColumn(name = "userId"))
  private Set<UserAccount> users;

用户:

@Entity
@Table(name = "UserAccounts")
public class UserAccount implements Serializable
{
  private static final long serialVersionUID = 1L;

  @Id
  @GeneratedValue(strategy = GenerationType.TABLE)
  @Column(name = "userId", nullable = false, unique = true)
  private Long id;

  @Column(name = "username", nullable = false, unique = true)
  private String username;

  @Column(name = "password", nullable = false)
  private String password;

  @ManyToMany(fetch = FetchType.EAGER)
  @JoinTable(name = "User_Book",
             joinColumns = @JoinColumn(name = "userId"),
             inverseJoinColumns = @JoinColumn(name = "bookId"))
  Set<Book> purchasedBooks;

一切正常，User_Book 表确实已在数据库中创建。问题似乎与访问此表有关。

例如，

Query query = entityManager.createQuery("SELECT u FROM User_Book u");

不断告诉我以下内容:

The abstract schema type 'User_Book' is unknown

那么，我应该从头开始创建 User_Book 实体吗？会不会像现在一样自动填充，即每当用户购买一本书时，是否会在表中记录这次购买？

Answer 1

User_Book 不是实体。因此你不能使用 createQuery , 但你可以使用 createNativeQuery执行 SQL 查询:

Query query = entityManager.createNativeQuery("SELECT * FROM User_Book");

结果将是 List<Object[]>