JPA關係對映系列四：many-to-many 關聯對映

weixin_33866037發表於2018-03-03

SpringDataJPA是Spring Data的一個子專案，通過提供基於JPA的Repository極大的減少了JPA作為資料訪問方案的程式碼量，你僅僅需要編寫一個介面整合下SpringDataJPA內部定義的介面即可完成簡單的CRUD操作。

前言

本篇文章引導你通過Spring Boot，Spring Data JPA和MySQL實現many-to-many關聯對映。

準備

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

技術棧

  • Spring Data JPA
  • Spring Boot
  • MySQL

目錄結構

[圖片上傳失敗...(image-6352f3-1520077140162)]

父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-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>

多對多關聯對映

目錄結構

[圖片上傳失敗...(image-e4badc-1520077140162)]

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-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>many-to-many</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</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>
多對多關聯

book.id 和 publisher.id 多對多關聯表book_publisher

2159429-51612d1e695b7ce3..png
https://raw.githubusercontent.com/longfeizheng/longfeizheng.github.io/master/images/jpa/spring-data-jpa09.png

db.sql

CREATE DATABASE  IF NOT EXISTS `jpa_manytomany`;
USE `jpa_manytomany`;

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

DROP TABLE IF EXISTS `book`;
CREATE TABLE `book` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;

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

DROP TABLE IF EXISTS `publisher`;
CREATE TABLE `publisher` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=19 DEFAULT CHARSET=utf8;
--
-- Table structure for table `book_publisher`
--

DROP TABLE IF EXISTS `book_publisher`;
CREATE TABLE `book_publisher` (
`book_id` int(10) unsigned NOT NULL,
`publisher_id` int(10) unsigned NOT 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;
實體類
Book
@Entity
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @ManyToMany(cascade = CascadeType.MERGE)
    @JoinTable(name = "book_publisher", joinColumns = @JoinColumn(name = "book_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "publisher_id", referencedColumnName = "id"))
    private Set<Publisher> publishers = new HashSet<>();

    public Book() {

    }

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

    public Book(String name, Set<Publisher> publishers) {
        this.name = name;
        this.publishers = publishers;
    }

    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<Publisher> getPublishers() {
        return publishers;
    }

    public void setPublishers(Set<Publisher> publishers) {
        this.publishers = publishers;
    }

    @Override
    public String toString() {
        String result = String.format(
                "Book [id=%d, name='%s']%n",
                id, name);
        if (publishers != null) {
            for (Publisher publisher : publishers) {
                result += String.format(
                        "Publisher[id=%d, name='%s']%n",
                        publisher.getId(), publisher.getName());
            }
        }

        return result;
    }
}
Publisher
@Entity
public class Publisher {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @ManyToMany(mappedBy = "publishers")
    private Set<Book> books = new HashSet<>();

    public Publisher(){

    }

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

    public Publisher(String name, Set<Book> books){
        this.name = name;
        this.books = books;
    }

    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<Book> getBooks() {
        return books;
    }

    public void setBooks(Set<Book> books) {
        this.books = books;
    }

    @Override
    public String toString() {
        String result = String.format(
                "Publisher [id=%d, name='%s']%n",
                id, name);
        if (books != null) {
            for(Book book : books) {
                result += String.format(
                        "Book[id=%d, name='%s']%n",
                        book.getId(), book.getName());
            }
        }

        return result;
    }
}

  • @Table宣告此物件對映到資料庫的資料表，通過它可以為實體指定表(talbe),目錄(Catalog)和schema的名字。該註釋不是必須的，如果沒有則系統使用預設值(實體的短類名)。

  • @Id 宣告此屬性為主鍵。該屬性值可以通過應該自身建立，但是Hibernate推薦通過Hibernate生成

  • @GeneratedValue 指定主鍵的生成策略。

    1. TABLE：使用表儲存id值
    2. IDENTITY：identitycolumn
    3. SEQUENCR ：sequence
    4. AUTO：根據資料庫的不同使用上面三個

  • @Column 宣告該屬性與資料庫欄位的對映關係。

  • @ManyToMany 多對多關聯關係

  • @JoinColumn 指定關聯的欄位

  • @JoinTable 參考

Spring Data JPA Repository
BookRepository
public interface BookRepository extends JpaRepository<Book, Integer> {
}
PublisherRepository
public interface PublisherRepository extends JpaRepository<Publisher, Integer> {
}

Spring Data JPA包含了一些內建的Repository，實現了一些常用的方法：findone，findall，save等。

application.yml
spring:
  datasource:
    url: jdbc:mysql://localhost/jpa_manytomany
    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
    public void saveTest() throws Exception {

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

        Book bookA = new Book("Book One");
        bookA.setPublishers(new HashSet<Publisher>() {{
            add(publisherA);
            add(publisherB);
        }});

        bookRepository.save(bookA);

    }

    @Test
    public void saveTest1() throws Exception{
        Publisher publisher = publisherRepository.findOne(24);
        Book bookA = new Book("Book Two");
        bookA.getPublishers().add(publisher);
        bookRepository.save(bookA);
    }

    @Test
    public void saveTest2() throws Exception{
        Book two = bookRepository.findOne(18);
        Publisher publisher = publisherRepository.findOne(25);
        two.getPublishers().add(publisher);
        bookRepository.save(two);
    }

    @Test
    public void findPublisherTest() throws Exception{
        Publisher publisher = publisherRepository.findOne(24);
        Set<Book> books = publisher.getBooks();
        for(Book book: books){
            log.info(book.getName()+"..."+book.getId());
        }
        Assert.assertNotNull(publisher);
        Assert.assertNotNull(publisher.getName());
    }

    @Test
    public void findAllTest() throws Exception {
        for (Book book : bookRepository.findAll()) {
            log.info(book.toString());
        }
    }

    @Test
    public void findBookTest() throws Exception{
        Book book = bookRepository.findOne(16);
        Set<Publisher> publishers = book.getPublishers();
        for(Publisher publisher: publishers){
            log.info(publisher.getName()+"..."+publisher.getId());
        }
        Assert.assertNotNull(book);
        Assert.assertNotNull(book.getName());
    }
}

程式碼下載

從我的 github 中下載，https://github.com/longfeizheng/jpa-example/tree/master/many-to-many

2159429-146fde9d845056c3..png
https://raw.githubusercontent.com/longfeizheng/longfeizheng.github.io/master/images/wechat/xiaochengxu.png

???關注微信小程式java架構師歷程
上下班的路上無聊嗎？還在看小說、新聞嗎？不知道怎樣提高自己的技術嗎？來吧這裡有你需要的java架構文章，1.5w+的java工程師都在看，你還在等什麼？

相關文章