java - 为什么 JpaRepository 在保存实体时尝试为空 FK 键创建实体？

Question

我有一个Person表，其中包含字段country(FK，可以为空)。当我尝试使用空的 国家/地区 值保存个人时，我会收到错误 500 和消息

2020-01-30 15:16:37.277 警告 10524 --- [nio-8098-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper:SQL 错误:0，SQLState:235022020-01-30 15:16:37.277 错误 10524 --- [nio-8098-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper : ОШИБКА: нулевое значение в столбце "code"нарушае т ограничение NOT NULL 答案: Ошибочная строка содержит (42，null，null，null)。2020-01-30 15:16:37.299 错误 10524 --- [nio-8098-exec-1] o.z.problem.spring.common.AdviceTraits:内部服务器错误

org.springframework.dao.DataIntegrityViolationException:无法执行语句； SQL [不适用]；约束[空]；嵌套异常是 org.hibernate.exception.ConstraintViolationException:无法执行语句

粗略错误推导:

Error: null value in "code" column breaks NOT NULL restriction Details: The error string contains (42, null, null, null).

Person.java

@Entity
@Table(name = "t_person")
@Data
public class Person {
    @Id
    @Column(name = "person_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    private String surname;
    private String name;
    private String patronymic;

    @Column(name = "surname_rus")
    private String surnameRus;

    @Column(name = "name_rus")
    private String nameRus;

    @Column(name = "surname_eng")
    private String surnameEng;

    @Column(name = "name_eng")
    private String nameEng;

    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "country_id")
    private Country country;

    private String settlement;
    private String occupation;

    @ManyToMany
    @JoinTable(
            name = "person_link",
            joinColumns = @JoinColumn(name = "person_id", referencedColumnName = "person_id"),
            inverseJoinColumns = @JoinColumn(name = "link_id", referencedColumnName = "link_id"))
    private List<UrlLink> linkList;

    @ManyToMany
    @JoinTable(
            name = "org_actor",
            joinColumns = @JoinColumn(name = "actor_id", referencedColumnName = "person_id"),
            inverseJoinColumns = @JoinColumn(name = "org_id", referencedColumnName = "org_id"))
    private List<Org> orgList;

    private String description;

    @ManyToMany
    @JoinTable(
            name = "person_hashtag",
            joinColumns = @JoinColumn(name = "person_id", referencedColumnName = "person_id"),
            inverseJoinColumns = @JoinColumn(name = "hashtag_id", referencedColumnName = "hashtag_id"))
    private List<HashTag> hashtagList;


************
Country.java

@Entity
@Table(name="t_country")
@Data

public class Country {
    @Id
    @Column(name = "country_id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private Integer id;
    private String code;
    private String name;
}

create table t_country
(
    country_id serial  not null
        constraint t_country_pkey
            primary key,
    code       char(3) not null
        constraint unique_constr_code
            unique,
    name       text
        constraint unique_constr_name
            unique,
    miscellany text,
    constraint constr_name
        unique (code, name)
);

如何保存国家为空的 Person 实体？

Answer 1

在您所在国家/地区的数据库表定义中，字段代码定义为

code
   char(3) not null
    constraint unique_constr_code
        unique,

表示数据库级别存在非空约束。

这就是为什么你无法拯救一个国家/地区为空字段的人。

因此，即使您在 java 代码中没有非空约束，数据库也会拒绝该值。也许您在删除 java 代码中的 not null 约束后忘记迁移数据库？