JPA关系映射系列三：one-to-many和many-to-one

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one-to-many和many-to-one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

<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>4.0.0modelVersion>

    <groupId>cn.merryyougroupId>
    <artifactId>jpa-exampleartifactId>
    <version>1.0-SNAPSHOTversion>
    <modules>
        <module>one-to-one-foreignkeymodule>
        <module>one-to-one-primarykeymodule>
        <module>one-to-manymodule>
        <module>many-to-manymodule>
        <module>many-to-many-extra-columnsmodule>
    modules>
    <packaging>pompackaging>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>io.spring.platformgroupId>
                <artifactId>platform-bomartifactId>
                <version>Brussels-SR6version>
                <type>pomtype>
                <scope>importscope>
            dependency>
        dependencies>
    dependencyManagement>
project>

一对多和多对一

目录结构

pom.xml

<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-exampleartifactId>
        <groupId>cn.merryyougroupId>
        <version>1.0-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>one-to-manyartifactId>

    <properties>
        <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
        <java.version>1.8java.version>
    properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-data-jpaartifactId>
        dependency>

        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <scope>runtimescope>
        dependency>

        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
            <scope>testscope>
        dependency>
    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
            plugin>
            <plugin>
                <groupId>org.apache.maven.pluginsgroupId>
                <artifactId>maven-compiler-pluginartifactId>
                <version>3.6.1version>
                <configuration>
                    <source>1.8source>
                    <target>1.8target>
                configuration>
            plugin>
        plugins>
    build>
project>

一对多和多对一关联

book.book-category_id 和 book_category.id

db.sql

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

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

DROP TABLE IF EXISTS `book_category`;
CREATE TABLE `book_category` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`,`name`)
) ENGINE=InnoDB AUTO_INCREMENT=9 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_category_id` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_book_bookcategoryid_idx` (`book_category_id`),
CONSTRAINT `fk_book_bookcategoryid` FOREIGN KEY (`book_category_id`) REFERENCES `book_category` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

实体类

Book

@Entity
public class Book {

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

    @ManyToOne
    @JoinColumn(name = "book_category_id")
    private BookCategory bookCategory;

    public Book() {

    }

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

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public BookCategory getBookCategory() {
        return bookCategory;
    }

    public void setBookCategory(BookCategory bookCategory) {
        this.bookCategory = bookCategory;
    }
}

BookCategory

@Entity
@Table(name = "book_category")
public class BookCategory {

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

    @OneToMany(mappedBy = "bookCategory", cascade = CascadeType.ALL)
    private Set books;

    public BookCategory(){

    }

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set getBooks() {
        return books;
    }

    public void setBooks(Set books) {
        this.books = books;
    }

    @Override
    public String toString() {
        String result = String.format(
                "Category[id=%d, name='%s']%n",
                id, name);
        if (books != null) {
            for(Book book : books) {
                result += String.format(
                        "Book[id=%d, name='%s']%n",
                        book.getId(), book.getName());
            }
        }

        return result;
    }

}

• @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。

• @OneToMany 一对多关联关系
• @ManyToOne 多对一关联关系
• @JoinColumn 指定关联的字段

Spring Data JPA Repository

public interface BookCategoryRepository extends JpaRepository<BookCategory, 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_onetomany
    username: root
    password: admin
    driver-class-name: com.mysql.jdbc.Driver
  jpa:
    show-sql: true
    properties:
      hibernate:
        enable_lazy_load_no_trans: true

BookRepositoryTest

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

    @Autowired
    private BookCategoryRepository repository;


    @Test
    public void saveCategoryTest(){
        BookCategory categoryOne = new BookCategory("Category One");
        Set books = new HashSet(){{
            add(new Book("Book One", categoryOne));
            add(new Book("Book Two", categoryOne));
            add(new Book("Book Three", categoryOne));
        }};
        categoryOne.setBooks(books);

        BookCategory categoryTwo = new BookCategory("Category Two");
        Set bookBs = new HashSet(){{
            add(new Book("Book Four", categoryTwo));
            add(new Book("Book Five", categoryTwo));
            add(new Book("Book Six", categoryTwo));
        }};
        categoryTwo.setBooks(bookBs);

        Set allBooks = new HashSet();

        allBooks.add(categoryOne);
        allBooks.add(categoryTwo);

        List list = repository.save(allBooks);

        Assert.assertNotNull(list);
    }

    @Test
    public void findAll() throws Exception{

        for (BookCategory bookCategory : repository.findAll()) {
            log.info(bookCategory.toString());
        }
    }
}

代码下载

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

---

������关注微信小程序java架构师历程
上下班的路上无聊吗？还在看小说、新闻吗？不知道怎样提高自己的技术吗？来吧这里有你需要的java架构文章，1.5w+的java工程师都在看，你还在等什么？