Question

我的数据库中有两个表，作者和书。这是它们两个的结构：

书桌：

@Entity
public class Book {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String title;

    @ManyToOne
    private Author author;

    ...getters and setters...
}

作者表：

@Entity
public class Author {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String name;

    ...getters and setters
}

我想通过该书的标题来获得特定书的作者。我已经在终端select author.name as author from author right join book on author.id = book.author_id where book.title='Some title';上使用此sql命令达到了此目的。如何在代码中构造查询以实现此目的？

Answer 1

这将是等效的查询

select a.name as author from author a right join book b where b.title = 'Some title'

用代码

entityManager.createQuery("select a.name as author from author a right join book b where b.title = ? ").setParameter(1, "Some title");

Answer 2

猜猜这比我想象的要容易得多。与其使用复杂的查询，我只是按照书名来获取这本书，然后按照其ID来获取作者，就像这样，它工作得很好：

Query query = manager.createQuery("select b from book b where b.title = :myTitle")
            .setParameter("myTitle", "Some title");

Book book = (Book) query.getSingleResult();
Author author = manager.find(Author.class, book.getAuthor().getId());

System.out.println(author.getName());

如何从Hibernate外键引用的表中获取值？

2 个答案: