JPA关系映射系列一:one-to-one外键关联

来源:转载


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"?>
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




一对一外键
目录结构


pom.xml
<?xml version="1.0" encoding="UTF-8"?>
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
one-to-one-foreignkey

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





一对一关系

book.book_detail_id 和 book_detail.id


db.sql


CREATE DATABASEIF 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 {
}

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 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 bookList = bookRepository.save(books);
Assert.assertNotNull(bookList);
Assert.assertEquals(3, bookList.size());
}
@Test
public void findBooksTest() throws Exception{
List 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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