如何在Spring JPA存储库方法中用@Query注释描述联接

Question

我在JPA和MySQL后端中使用Spring-Boot。现在，我对Spring-Boot提供的存储库感到非常困惑。我知道这些功能非常强大（而且似乎非常有用，因为它们可以大大缩短代码）。但是，我不明白如何表示它们中的联接，因为结果集应该是选择几个实体中指定属性的组合。

现在假设我们有三个表book、author、authorofbook，其中最后一个表通过一个组合的主键简单地连接book和author。我想我们有以下Java类：

@Entity
@Table(name="BOOK")
public class Book {

  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "ID")
  private int id;
  @Column(name = "TITLE")
  private String title;

}

@Entity
@Table(name="AUTHOR")
public class Author {

  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "ID")
  private int id;
  @Column(name = "LASTNAME")
  private String lastname;
  @Column(name = "FIRSTNAME")
  private String firstname;
  //Let's assume some getters and setters and a constructor
}

@Entity
@Table(name="BOOK")
public class Book {
  @EmbeddedId
  private AuthorOfBookId pk;
}

@Embeddable
public class AuthorOfBookId implements Serializable {
  private int authorId;
  private int bookId;
}

@Repository
public interface AuthorOfBookRepository extends JpaRepository<,AuthorOfBookId> {

}

SELECT b.name, a.firstname, a.lastname from AuthorOfBook ab inner join Book b on b.id = ab.book_id inner join Author a on a.id = ab.author_id where a.lastname = :lastname;

@Query([the query string from above])
public (...) findAuthorAndBookByAuthorLastname(@Param("lastname") String lastname);

Answer 1

您不希望authorofbook作为一个单独的实体。book应该有一个author类型的字段作为@manytoone关系。这样，给定任何书，您都可以找到作者的详细信息。