JPA关系映射系列二：one-to-one主键关联

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 实现一对一主键关联映射。

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>

一对一主键

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-primarykey</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>

一对一主键关联

book.id 和 book_detail.book_id

db.sql

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

--
-- Table structure for table `book_detail`
--
DROP TABLE IF EXISTS `book`;
CREATE TABLE `book` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8;

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

DROP TABLE IF EXISTS `book_detail`;
CREATE TABLE `book_detail` (
`book_id` int(11) unsigned NOT NULL,
`number_of_pages` int(11) DEFAULT NULL,
PRIMARY KEY (`book_id`),
CONSTRAINT `fk_bookdetail_bookid` FOREIGN KEY (`book_id`) REFERENCES `book` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

实体类

Book

@Entity
@Data
public class Book implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String name;
    @OneToOne(cascade = CascadeType.ALL, mappedBy = "book")
    private BookDetail bookDetail;

    public Book() {

    }

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

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

    @Override
    public String toString() {
        return String.format(
                "Book[id=%d, name='%s', number of pages='%d']",
                id, name, bookDetail.getNumberOfPages());
    }
}

BookDetail

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

    @Id
    @OneToOne
    @JoinColumn(name = "book_id")
    private Book book;

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

    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_primarykey
    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 saveTestPrimaryKey() 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)));
        bookRepository.save(books);
    }

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