JPA Relational Mapping Series 5: Many-to-many relational tables have additional field relational mappings

Father pom. XML

<?xml version="1.0" encoding="UTF-8"? >
<project 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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>cn.merryyou</groupId>
    <artifactId>jpa-example</artifactId>
    <version>1.0 the SNAPSHOT</version>
    <modules>
        <module>one-to-one-foreignkey</module>
        <module>one-to-one-primarykey</module>
        <module>one-to-many</module>
        <module>many-to-many</module>
        <module>many-to-many-extra-columns</module>
    </modules>
    <packaging>pom</packaging>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>io.spring.platform</groupId>
                <artifactId>platform-bom</artifactId>
                <version>Brussels-SR6</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>
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Many-to-many association mapping

The directory structure

pom.xml

<?xml version="1.0" encoding="UTF-8"? >
<project 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">
    <parent>
        <artifactId>jpa-example</artifactId>
        <groupId>cn.merryyou</groupId>
        <version>1.0 the SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>many-to-many-extra-columns</artifactId>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1 track</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>
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Many-to-many association

Book. id and publisher.id many-to-many association tables book_publisher also have the published_data field

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;

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Entity class

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(a) {}public Book(String name) {
        this.name = name;
        bookPublishers = new HashSet<>();
    }

    public int getId(a) {
        return id;
    }

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

    public String getName(a) {
        return name;
    }

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

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

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

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

    public int getId(a) {
        return id;
    }

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

    public String getName(a) {
        return name;
    }

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

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

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

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(a) {
        return book;
    }

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


    public Publisher getPublisher(a) {
        return publisher;
    }

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

    public Date getPublishedDate(a) {
        return publishedDate;
    }

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

• @table declares the Table of data that this object maps to the database by specifying the names of tables (TALbe), directories (Catalog), and schemas for entities. This annotation is not required; if not, the system uses the default (the short class name of the entity).

• @id declares this property as the primary key. This attribute value can be created by itself, but Hibernate recommends that it be generated by Hibernate

• @GeneratedValue specifies the primary key generation strategy.

  1. TABLE: Uses a TABLE to store id values
  2. IDENTITY: identitycolumn
  3. SEQUENCR ：sequence
  4. AUTO: Use the preceding three parameters based on the database

• @column declares the mapping of this property to a database field.

• @onetomany One-to-many association relationship

• @manytomany Many-to-many association relationships

• @joinColumn Specifies the associated field

• @ JoinTable reference

Spring Data JPA Repository

BookRepository

public interface BookRepository extends JpaRepository<Book.Integer> {}Copy the code

PublisherRepository

public interface PublisherRepository extends JpaRepository<Publisher.Integer> {}Copy the code

Spring Data JPA includes built-in repositories that implement common methods: Findone, FindAll, Save, etc.

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
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BookRepositoryTest

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

    @Autowired
    private BookRepository bookRepository;

    @Autowired
    private PublisherRepository publisherRepository;


    @Test
    @Transactional
    public void manyToManyExtraColumnsTest(a) 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);

        // testSystem.out.println(bookA.getBookPublishers().size()); }}Copy the code

The code download

Download it from my Github, github.com/longfeizhen…

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