为什么 Hibernate 不创建多对多连接表？答案

【问题标题】：Why is Hibernate not creating many-to-many join tables?为什么 Hibernate 不创建多对多连接表？
【发布时间】：2022-01-20 17:27:40
【问题描述】：

我正在尝试让 Hibernate 创建一个多对多关系连接表。实体表创建得很好，但连接表不会显示。一些来源手动创建连接表，其他来源（如 Youtube 教程）解释了它们是如何由 Hibernate 自动创建的。

这是我的第一个实体表：

package com.presents;
import javax.persistence.*;
import java.io.Serial;
import java.io.Serializable;
import java.util.Set;

 @Entity
 @Table(name = "articles")
 public class Article implements Serializable {

@Serial
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id")
private int id;

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

@Column(name = "link")
private String url;

@Column(name = "likes")
private int likes;

@Column(name = "clicks")
private int clicks;

@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
        name = "category_article",
        joinColumns = {
                @JoinColumn(name = "article_id", referencedColumnName = "id")
        },
        inverseJoinColumns =  {
                @JoinColumn(name = "category_id", referencedColumnName = "id")
        }
)
public Set<Categories> categories = new HashSet<>();;


public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getUrl() {
    return url;
}

public void setUrl(String url) {
    this.url = url;
}

public int getLikes() {
    return likes;
}

public void setLikes(int likes) {
    this.likes = likes;
}

public int getClicks() {
    return clicks;
}

public void setClicks(int clicks) {
    this.clicks = clicks;
}

public Set<Categories> getCategories() {
    return cats;
}

public void setCategories(Set<Categories> categories) {
    this.cats = categories;
}

}

这是我的第二个实体表：

包 com.presents;

import javax.persistence.*;
import java.io.Serial;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

@Entity
@Table(name = "category")
public class Categories implements Serializable {

@Serial
private static final long serialVersionUID = 1L;


@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name = "id")
private int id;

@Column(name = "category")
private String category;

@ManyToMany(mappedBy = "categories")
public Set<Article> articles = new HashSet<>();

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public void setCategory(String category) {
    this.category = category;
}

public String getCategory() {
    return category;
}

public void setArticles(Set<Article> articles) {
    this.articles = articles;
}

public Set<Article> getArticles() {
    return articles;
}

}

这个想法是任何文章都可以属于许多类别，但不止一个类别可以适用于任何文章。

我使用的是 SQLite3 数据库，但我也尝试使用 MySQL 数据库，但均无济于事。 Hibernate 似乎以某种方式完全避免了多对多注释。当我运行代码时它并没有抱怨它，并且似乎完全避免了它。再一次，另一个表的创建很漂亮，没有我用任何 SQL 命令摸索。为什么 Hibernate 拒绝创建连接表，我该如何解决？

这是Hibernate的输出：

INFO: HHH000412: Hibernate ORM core version 5.6.2.Final
Dez. 18, 2021 8:41:14 AM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
Dez. 18, 2021 8:41:15 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
Dez. 18, 2021 8:41:15 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [org.sqlite.JDBC] at URL [jdbc:sqlite:presents.db]
Dez. 18, 2021 8:41:15 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {}
Dez. 18, 2021 8:41:15 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Dez. 18, 2021 8:41:15 AM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
Dez. 18, 2021 8:41:15 AM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.SQLiteDialect
Hibernate: drop table if exists articles
Hibernate: drop table if exists category
Hibernate: drop table if exists hibernate_sequence
Hibernate: create table articles (id integer not null, name varchar, link varchar, likes integer, clicks integer, primary key (id))
Hibernate: create table category (id integer not null, category varchar, primary key (id))
Hibernate: create table hibernate_sequence (next_val bigint)
Hibernate: insert into hibernate_sequence values ( 1 )
Dez. 18, 2021 8:41:16 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@334ebcaa] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Dez. 18, 2021 8:41:16 AM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@107bfcb2] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Dez. 18, 2021 8:41:16 AM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator initiateService
INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: select next_val as id_val from hibernate_sequence
Hibernate: update hibernate_sequence set next_val= ? where next_val=?
Hibernate: insert into articles (name, link, likes, clicks, id) values (?, ?, ?, ?, ?)
Hibernate: insert into articles (name, link, likes, clicks, id) values (?, ?, ?, ?, ?)
Hibernate: insert into articles (name, link, likes, clicks, id) values (?, ?, ?, ?, ?)
Hibernate: insert into articles (name, link, likes, clicks, id) values (?, ?, ?, ?, ?)
Hibernate: insert into category (category, id) values (?, ?)
Hibernate: insert into category (category, id) values (?, ?)
Hibernate: insert into category (category, id) values (?, ?)
Hibernate: select categories0_.id as id1_1_, categories0_.category as category2_1_ from category categories0_

【问题讨论】：

为 spring.jpa.hibernate.ddl-auto 选择了什么值？ “create-drop”或“update”或嗯……别的什么？设置spring.jpa.hibernate.show-sql=true，找到建表日志。这个表有日志吗？
我不使用 Spring。 hbm2ddl.auto 设置为 create-drop。上面，我为表格添加了日志。

标签： java sql hibernate jpa persistence

【解决方案1】：

我自己发现了错误。当我应该使用 Hibernate XML 映射时，我正在使用 JPA 注释。删除所有注释并在 XML 映射文件中创建必要的行后，表格出现了。

【讨论】：

【解决方案2】：

您需要获取一篇文章，然后添加一个类别并保存它。例如：

Categories category = categoryRepository.getById(100001);
article.getCategories().add(category);
articlesRepository.save(article);
productRepository.findAll();

这将在 category_article 表中添加一个新条目。

【讨论】：