如何在Spring Boot中连接SQL表？

Question

如何将类author中的author\u firstName和author\u lastName与类目绑定？我使用h2数据库，作者id和图书id是主键，我使用postman

public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "book_id")
    private int id;
    @Column(name = "book_title")
    private String title;
    @Column(name = "book_genre")
    private String genre;
    @Column(name = "author")
    private String author;

}

@Entity
@Table(name="Author")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Author {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="author_id")
    private int authorId;
    
    @Column(name="author_firstName")
    private String firstName;
    
    @Column(name="author_lastName")
    private String lastName;
    @Column(name="author_birth")
    private Date birth;

}

Answer 1

您应该将其转换为@manytone关系，而不是将字符串参数用于author：

@Entity
@Table(name="Author")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Author {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="author_id")
    private int authorId;
    
    @Column(name="author_firstName")
    private String firstName;
    
    @Column(name="author_lastName")
    private String lastName;
    @Column(name="author_birth")
    private Date birth;

    @OneToMany(mappedBy = "author")
    private List<Book> books;

}

@Entity
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "book_id")
    private int id;
    @Column(name = "book_title")
    private String title;
    @Column(name = "book_genre")
    private String genre;

    @ManyToOne
    @JoinColumn(name = "author_id")
    private Author author;

}

使用此模型，您将能够从任何入口点、从作者（由特定作者编写的书籍）或拥有书籍的作者（由作者编写的书籍集合）的书籍中获取数据。

您可以使用findAllSpring Data JPA实现的默认实现（如果您使用EAGER读取类型，将自动加入这两个表），或者构建您自己的JPQL：

作者a FETCH JOINa.booksb WHEREa.id=b.author。

这将有助于提高代码的易读性，并改进数据库数据规范化。