JPA關係對映系列三：one-to-many和many-to-one
阿新 • • 發佈：2019-01-29
SpringDataJPA是Spring Data的一個子專案，通過提供基於JPA的Repository極大的減少了JPA作為資料訪問方案的程式碼量，你僅僅需要編寫一個介面整合下SpringDataJPA內部定義的介面即可完成簡單的CRUD操作。
前言
本篇文章引導你通過Spring Boot，Spring Data JPA和MySQL實現one-to-many和many-to-one關聯對映。
準備
- JDK 1.8 或更高版本
- Maven 3 或更高版本
- MySQL Server 5.6
技術棧
- Spring Data JPA
- Spring Boot
- MySQL
目錄結構
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> 一對多和多對一
目錄結構
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-many</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>一對多和多對一關聯
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;實體類
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<Book> 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<Book> getBooks() {
return books;
}
public void setBooks(Set<Book> 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宣告此物件對映到資料庫的資料表，通過它可以為實體指定表(talbe),目錄(Catalog)和schema的名字。該註釋不是必須的，如果沒有則系統使用預設值(實體的短類名)。@Id宣告此屬性為主鍵。該屬性值可以通過應該自身建立，但是Hibernate推薦通過Hibernate生成@GeneratedValue指定主鍵的生成策略。- TABLE：使用表儲存id值
- IDENTITY：identitycolumn
- SEQUENCR ：sequence
- AUTO：根據資料庫的不同使用上面三個
@Column宣告該屬性與資料庫欄位的對映關係。@OneToMany一對多關聯關係@ManyToOne多對一關聯關係@JoinColumn指定關聯的欄位
Spring Data JPA Repository
public interface BookCategoryRepository extends JpaRepository<BookCategory, Integer> {
}Spring Data JPA包含了一些內建的Repository，實現了一些常用的方法：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: trueBookRepositoryTest
@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<Book>(){{
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<Book>(){{
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());
}
}
}程式碼下載
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