JPA关系映射系列五：many-to-many 关联表存在额外字段关系映射

SpringDataJPA是Spring Data的一个子项目，通过提供基于JPA的Repository极大的减少了JPA作为数据访问方案的代码量，你仅仅需要编写一个接口集成下SpringDataJPA内部定义的接口即可完成简单的CRUD操作。

前言

本篇文章引导你通过Spring Boot，Spring Data JPA和MySQL实现many-to-many关联表存在额外字段下关系映射。

准备

• JDK 1.8 或更高版本
• Maven 3 或更高版本
• MySQL Server 5.6

技术栈

• Spring Data JPA
• Spring Boot
• MySQL

目录结构

父pom.xml

 xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    4.0.0

    cn.merryyou
    jpa-example
    1.0-SNAPSHOT
    
        one-to-one-foreignkey
        one-to-one-primarykey
        one-to-many
        many-to-many
        many-to-many-extra-columns
    
    pom


    
        
            
                io.spring.platform
                platform-bom
                Brussels-SR6
                pom
                import
            
        
    

多对多关联映射

目录结构

pom.xml

 xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    
        jpa-example
        cn.merryyou
        1.0-SNAPSHOT
    
    4.0.0

    many-to-many-extra-columns

    
        UTF-8
        1.8
    

    
        
            org.springframework.boot
            spring-boot-starter-data-jpa
        

        
            mysql
            mysql-connector-java
            runtime
        

        
            org.projectlombok
            lombok
        

        
            org.springframework.boot
            spring-boot-starter-test
            test
        
    

    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
            
                org.apache.maven.plugins
                maven-compiler-plugin
                3.6.1
                
                    1.8
                    1.8
                
            
        
    

多对多关联

book.id 和 publisher.id 多对多关联表book_publisher还存在published_data字段 

db.sql

CREATE DATABASE  IF NOT EXISTS `jpa_manytomany_extracolumns` /*!40100 DEFAULT CHARACTER SET utf8 */;
USE `jpa_manytomany_extracolumns`;

--
-- Table structure for table `book`
--

DROP TABLE IF EXISTS `book`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `book` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Table structure for table `publisher`
--

DROP TABLE IF EXISTS `publisher`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `publisher` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=21 DEFAULT CHARSET=utf8;

--
-- Table structure for table `book_publisher`
--

DROP TABLE IF EXISTS `book_publisher`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `book_publisher` (
`book_id` int(10) unsigned NOT NULL,
`publisher_id` int(10) unsigned NOT NULL,
`published_date` datetime DEFAULT NULL,
PRIMARY KEY (`book_id`,`publisher_id`),
KEY `fk_bookpublisher_publisher_idx` (`publisher_id`),
CONSTRAINT `fk_bookpublisher_book` FOREIGN KEY (`book_id`) REFERENCES `book` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_bookpublisher_publisher` FOREIGN KEY (`publisher_id`) REFERENCES `publisher` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

实体类

Book

@Entity
public class Book{

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

    @OneToMany(mappedBy = "book", cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<BookPublisher> bookPublishers;

    public Book() {
    }

    public Book(String name) {
        this.name = name;
        bookPublishers = 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 Set<BookPublisher> getBookPublishers() {
        return bookPublishers;
    }

    public void setBookPublishers(Set<BookPublisher> bookPublishers) {
        this.bookPublishers = bookPublishers;
    }
}

Publisher

@Entity
public class Publisher {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @OneToMany(mappedBy = "publisher")
    private Set<BookPublisher> bookPublishers;

    public Publisher(){

    }

    public Publisher(String name){
        this.name = name;
    }

    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 Set<BookPublisher> getBookPublishers() {
        return bookPublishers;
    }

    public void setBookPublishers(Set<BookPublisher> bookPublishers) {
        this.bookPublishers = bookPublishers;
    }
}

BookPublisher

@Entity
@Table(name = "book_publisher")
public class BookPublisher implements Serializable {

    @Id
    @ManyToOne
    @JoinColumn(name = "book_id")
    private Book book;

    @Id
    @ManyToOne
    @JoinColumn(name = "publisher_id")
    private Publisher publisher;

    @Column(name = "published_date")
    private Date publishedDate;

    public Book getBook() {
        return book;
    }

    public void setBook(Book book) {
        this.book = book;
    }


    public Publisher getPublisher() {
        return publisher;
    }

    public void setPublisher(Publisher publisher) {
        this.publisher = publisher;
    }

    public Date getPublishedDate() {
        return publishedDate;
    }

    public void setPublishedDate(Date publishedDate) {
        this.publishedDate = publishedDate;
    }
}

• @Table声明此对象映射到数据库的数据表，通过它可以为实体指定表(talbe),目录(Catalog)和schema的名字。该注释不是必须的，如果没有则系统使用默认值(实体的短类名)。
• @Id 声明此属性为主键。该属性值可以通过应该自身创建，但是Hibernate推荐通过Hibernate生成
• @GeneratedValue 指定主键的生成策略。
  1. TABLE：使用表保存id值
  2. IDENTITY：identitycolumn
  3. SEQUENCR ：sequence
  4. AUTO：根据数据库的不同使用上面三个
• @Column 声明该属性与数据库字段的映射关系。
• @OneToMany 一对多关联关系
• @ManyToMany 多对多关联关系
• @JoinColumn 指定关联的字段
• @JoinTable 参考

Spring Data JPA Repository

BookRepository

public interface BookRepository extends JpaRepository<Book, Integer> {
}

PublisherRepository

public interface PublisherRepository extends JpaRepository<Publisher, Integer> {
}

Spring Data JPA包含了一些内置的Repository，实现了一些常用的方法：findone，findall，save等。

application.yml

spring:
  datasource:
    url: jdbc:mysql://localhost/jpa_manytomany_extracolumns
    username: root
    password: admin
    driver-class-name: com.mysql.jdbc.Driver
  jpa:
    show-sql: true
    properties:
      hibernate:
        enable_lazy_load_no_trans: true

BookRepositoryTest

@RunWith(SpringRunner.class)
@SpringBootTest
@Slf4j
public class BookRepositoryTest {

    @Autowired
    private BookRepository bookRepository;

    @Autowired
    private PublisherRepository publisherRepository;


    @Test
    @Transactional
    public void manyToManyExtraColumnsTest() throws Exception{
        Book bookA = new Book("Book One");

        Publisher publisherA = new Publisher("Publisher One");

        BookPublisher bookPublisher = new BookPublisher();
        bookPublisher.setBook(bookA);
        bookPublisher.setPublisher(publisherA);
        bookPublisher.setPublishedDate(new Date());
        bookA.getBookPublishers().add(bookPublisher);

        publisherRepository.save(publisherA);
        bookRepository.save(bookA);

        // test
        System.out.println(bookA.getBookPublishers().size());

        // update
        bookA.getBookPublishers().remove(bookPublisher);
        bookRepository.save(bookA);

        // test
        System.out.println(bookA.getBookPublishers().size());
    }

}

代码下载

从我的 github 中下载，https://github.com/longfeizheng/jpa-example/tree/master/many-to-many-extra-columns

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