Preface

This article guides you through Spring Boot, Spring Data JPA and MySQL to map one-to-one foreign keys, one-to-one primary keys, one-to-many, many-to-many, many-to-many, many-to-many additional columns.

Get ready

• JDK 1.8 or later
• Maven 3 or later
• MySQL Server 5.6

technology stack

• Spring Data JPA
• Spring Boot
• MySQL

directory structure

Father 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>

One-to-one foreign key

directory structure

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>

One-to-one relationship

book.book_detail_id and 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;

Entity class

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;
    }
}

• The @Table declares that this object maps to the database's data tables by which the names of tables (talbe), catalogs, and schema s can be specified for entities. This annotation is not required, and if not, the system uses the default value (the short class name of the entity).

• Id declares this property as the primary key. This attribute value can be created by itself, but Hibernate recommends that it be generated by Hibernate

• GeneratedValue specifies the primary key generation strategy.

  1. TABLE: Save id values with tables
  2. IDENTITY: identitycolumn
  3. SEQUENCR : sequence
  4. AUTO: The three above are used differently depending on the database.

• Column declares the mapping relationship between the attribute and the database field.

• OneToOne One One-to-one Association

• JoinColumn specifies the associated fields

Spring Data JPA Repository

public interface BookRepository extends JpaRepository<Book, Integer> {
}

Spring Data JPA includes some built-in Repository and implements some commonly used methods: findone, findall, save, etc.

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<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());
    }

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

}

Other

The remaining one-to-one primary key, one-to-many, many-to-one, many-to-many, many-to-many additional column references are as above.

Code download

Download it from my github. https://github.com/longfeizheng/jpa-example