Question

我正在使用Spring-Boot，Hibernate和MariaDB。我有一个book实体和一个author实体，并通过双向book_authors关联将它们映射到@manytomany表。似乎已使用适当的外键约束创建了联接表，但是，当我向其各自的表中添加作者然后再添加书籍时，并不会填充联接表。我将ddl-auto设置为validate，所以该表没有被覆盖。我可以看到由hibernate生成的sql join语句，当我手动运行它时，它会拉正确的列，但我从未看到insert语句。我也尝试了CascadeTypes的几种不同组合，但是不确定为什么休眠不保留数据。

最初，每个实体都由单独的微服务bookmsvc和authormsvc管理，但是在遇到manytomany关联问题后，我将两个实体都复制到了两个微服务中。我不确定这是否必要或最佳做法。我的工作流程为：

启动authormsvc，创建表。
启动bookmsvc，删除并重新创建表。
杀死这两个服务，更改ddl-auto以进行验证，然后重新启动微服务。
通过api插入作者。
通过api插入书。

在这一点上，我希望可以填充联接表。我确定我有一个基本的误解，但是我不确定这是什么。我读过最好使用两个onetomany / manytoone关联，但是我不确定这是否准确反映了这种关系？有更好的方法吗？

如果没有，我如何进入休眠状态以填充联接表？

作者

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

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

    @NotNull @Column(name = "author_name")
  private String authorName;

    @ManyToMany( mappedBy = "authors",
      fetch   = FetchType.LAZY,
      cascade = { CascadeType.PERSIST, CascadeType.MERGE })
  public List<Book> books = new ArrayList<>();

  public Author() {}

  public Long getId() {
    return id;
  }
  public String getAuthorName() {
    return authorName;
  }

  public void setId(Long id) {
    this.id = id;
  }
  public void setName(String name) {
    this.authorName = name;
  }
}

图书

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


      @Id
      @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

      @NotNull @Column(name = "title")
    private String title;

      @NotNull @Column(name = "pub_id")
  private Long pubId;

      @NotNull @Column(name = "auth_id")
  private Long authId;

    @ManyToMany(
      fetch   = FetchType.LAZY,
      cascade = { CascadeType.PERSIST, CascadeType.MERGE })
    @JoinTable(name = "book_authors",
      joinColumns = {
        @JoinColumn(
            name = "book_id",
            referencedColumnName = "id"          
        )
      },
      inverseJoinColumns = {
        @JoinColumn(
            name = "auth_id",
            referencedColumnName = "id"          
        )
      })
  public List<Author> authors = new ArrayList<>();

  public Book() {}


  public Long getId() {
    return id;
  }
  public String getTitle() {
    return title;
  }
  public Long getPubId() {
    return pubId;
  }
  public Long getAuthId() {
    return authId;
  }


  public void setId(Long id) {
    this.id = id;
  }
  public void setTitle(String title) {
    this.title = title;
  }
  public void setPubId(Long pubId) {
    this.pubId = pubId;
  }
  public void setAuthId(Long authId) {
    this.authId = authId;
  }
}

由休眠生成的SQL

create table author (id bigint not null auto_increment, author_name varchar(255) not null, primary key (id)) engine=MyISAM

create table book (id bigint not null auto_increment, auth_id bigint not null, pub_id bigint not null, title varchar(255) not null, primary key (id)) engine=MyISAM

create table book_authors (book_id bigint not null, auth_id bigint not null) engine=MyISAM

alter table book_authors add constraint FKo21n38yco1hp4gvkb1xobm5vx foreign key (auth_id) references author (id)

alter table book_authors add constraint FK9s79v70m4fxo4c0qigpn5daf8 foreign key (book_id) references book (id)

select authors0_.book_id as book_id1_2_0_, authors0_.auth_id as auth_id2_2_0_, author1_.id as id1_0_1_, author1_.author_name as author_n2_0_1_ from book_authors authors0_ inner join author author1_ on authors0_.auth_id=author1_.id where authors0_.book_id=?

book_authors表

MariaDB [lms]> describe book_authors;
+---------+------------+------+-----+---------+-------+
| Field   | Type       | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| book_id | bigint(20) | NO   | MUL | NULL    |       |
| auth_id | bigint(20) | NO   | PRI | NULL    |       |
+---------+------------+------+-----+---------+-------+
2 rows in set (0.002 sec)

MariaDB [lms]> select * from book_authors;
Empty set (0.001 sec)

休眠-连接表数据不持久

0 个答案: