JPA关系映射系列二：one-to-one主键关联-白红宇

JPA关系映射系列二：one-to-one主键关联

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发布时间：2019-06-27

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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


    
        
     
      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

一对一主键

目录结构

pom.xml


    
        
             
      
       jpa-example
              
      
       cn.merryyou
              
      
       1.0-SNAPSHOT
          
         
     
      4.0.0
         
     
      one-to-one-primarykey
         
             
      
       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@Datapublic 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")@Datapublic 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
    
      {}

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()@Slf4jpublic class BookRepositoryTest {    @Autowired    private BookRepository bookRepository;    @Test    public void saveTestPrimaryKey() 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)));        bookRepository.save(books);    }    @Test    public void findBooksTestPrimaryKey() throws Exception{        List
     
       books = bookRepository.findAll();        for (Book book: books) {            log.info(book.toString());        }    }}