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实现一对一外键关联映射。

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

<?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。

  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。

• @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_foreignkeyusername: rootpassword: admindriver-class-name: com.mysql.jdbc.Driverjpa:show-sql: true

BookRepositoryTest

@RunWith(SpringRunner.class)
@SpringBootTest
@Slf4j
public class BookRepositoryTest {@Autowiredprivate BookRepository bookRepository;@Testpublic 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());}@Testpublic void findBooksTest() throws Exception{List<Book> books = bookRepository.findAll();for (Book book: books) {log.info(book.toString());}}}

代码下载

从我的 github 中下载，https://github.com/longfeizheng/jpa-example/tree/master/one-to-one-foreignkey

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