JPA关系映射之one-to-one、one-to-many、many-to-one和many-to-many

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

映射一对一外键、一对一主键、一对多，多对一，多对多、多对多额外的列的关系。

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

<?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>

一对一外键

目录结构





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>one-to-one-foreignkey</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>

一对一关系

book.book_detail_id

和

book_detail.id

db.sql

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

--
-- Table structure for table `book_detail`
--

DROP TABLE IF EXISTS `book_detail`;
CREATE TABLE `book_detail` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`number_of_pages` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

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

DROP TABLE IF EXISTS `book`;
CREATE TABLE `book` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
`book_detail_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_book_bookdetail` (`book_detail_id`),
CONSTRAINT `fk_book_bookdetail` FOREIGN KEY (`book_detail_id`) REFERENCES `book_detail` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

实体类

Book

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

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

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

@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "book_detail_id")
//    @Lazy(false)
private BookDetail bookDetail;

public Book() {
}

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

BookDetail

@Entity
@Table(name = "book_detail")
@Data
public class BookDetail {

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

@Column(name = "number_of_pages")
private Integer numberOfPages;

@OneToOne(mappedBy = "bookDetail")
private Book book;

public BookDetail() {
}

public BookDetail(Integer numberOfPages) {
this.numberOfPages = numberOfPages;
}
}

@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。

TABLE：使用表保存id值

IDENTITY：identitycolumn

SEQUENCR ：sequence

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。

@OneToOne

一对一关联关系

@JoinColumn

指定关联的字段

Spring Data JPA Repository

public interface BookRepository extends JpaRepository<Book, 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_onetoone_foreignkey
username: root
password: admin
driver-class-name: com.mysql.jdbc.Driver
jpa:
show-sql: true

BookRepositoryTest

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

@Autowired
private BookRepository bookRepository;

@Test
public void saveTest() throws Exception {

List<Book> books = new ArrayList<>();
books.add(new Book("Book one", new BookDetail(1)));
books.add(new Book("Book two", new BookDetail(2)));
books.add(new Book("Book three", new BookDetail(3)));
List<Book> bookList = bookRepository.save(books);
Assert.assertNotNull(bookList);
Assert.assertEquals(3, bookList.size());
}

@Test
public void findBooksTest() throws Exception{
List<Book> books = bookRepository.findAll();
for (Book book: books) {
log.info(book.toString());
}
}

}

其它

剩下的一对一主键、一对多，多对一，多对多、多对多额外的列参考如上。

代码下载

从我的 github 中下载，https://github.com/longfeizheng/jpa-example