无法执行SQL语句

Question

在编写我的应用程序时，我遇到了执行SQL语句的问题。我试图在网上寻找解决方案，但没有找到帮助，我仍然不知道如何处理我得到的错误。这是我得到的例外：

org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint ["FKAM8LLDERP40MVBBWCEQPU6L2S: PUBLIC.BOOK_CATEGORY FOREIGN KEY(CATEGORY_ID) REFERENCES PUBLIC.CATEGORY(ID) (2)"; SQL statement:
insert into book_category (book_id, category_id) values (?, ?) [23506-196]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement

这就是类的外观：Book.class

@Entity
@Table(name = "book")
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(nullable = false)
    private String title;
    private String description;
    @Column(name = "release_date")
    @Temporal(TemporalType.TIMESTAMP)
    private Date releaseDate;
    @JoinColumn(name = "cover_image")
    @OneToOne(cascade = CascadeType.MERGE)
    private UploadFile coverImage;
    @OneToOne(cascade = CascadeType.MERGE)
    private UploadFile content;
    @ManyToMany
    @JoinTable(name = "book_category", joinColumns = {@JoinColumn(name = "book_id", referencedColumnName = "id")},
        inverseJoinColumns = {@JoinColumn(name = "category_id", referencedColumnName = "id")})
    private Set<Category> categories;

    // constructors, setters, getters

}

Category.class

@Entity
@Table(name = "category")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "category_name")
    private String name;
    @ManyToMany(mappedBy = "categories", fetch = FetchType.LAZY)
    private List<Book> books;

    // ...
}

Answer 1

你在那里缺少cascade的定义。

您的图书类别在首先插入引用的实体（书籍或类别）之前编写。由于您指定的约束，因此不允许这样做。解决方案是定义

cascade = CascadeType.ALL

在连接的两侧（包括书籍和类别）。这将确保JPA以正确的顺序保留所有实体。