通过JPA进行简单的(内)连接查询
1.准备
1.1开发工具Intellij Idea
1.2数据库mysql
1.3新建Spring Initializr项目，勾选web,mysql,rest,jpa依赖
2.开始
2.1项目结构
2.2pom.xml内容
<?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>com.example</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.6.RELEASE</version>
<relativePath/>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</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>
</plugins>
</build>
</project>
2.3Author类内容；
package com.example.demo;
import javax.persistence.*;
import java.util.List;
@Entity
public class Author {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int Id;
private String name;
private int age;
@OneToMany( mappedBy = "author" )
private List<Book> books;
public void setId(int id) {
Id = id;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public void setBooks(List<Book> books) {
this.books = books;
}
public int getId() {
return Id;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public List<Book> getBooks() {
return books;
}
}
2.4Book类内容：
package com.example.demo;
import javax.persistence.*;
@Entity
public class Book {
@javax.persistence.Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int Id;
private String name;
private float price;
@JoinColumn
@ManyToOne(cascade = CascadeType.ALL)
private Author author;
public void setId(int id) {
Id = id;
}
public void setName(String name) {
this.name = name;
}
public void setPrice(float price) {
this.price = price;
}
public void setAuthor(Author author) {
this.author = author;
}
public int getId() {
return Id;
}
public String getName() {
return name;
}
public float getPrice() {
return price;
}
public Author getAuthor() {
return author;
}
}
2.5BookRepository接口内容：
package com.example.demo;
import org.springframework.data.repository.CrudRepository;
public interface AuthorRepository extends CrudRepository<Author,Integer> {
}
2.6AuthorRepository接口内容：
package com.example.demo;
import org.springframework.data.repository.CrudRepository;
public interface BookRepository extends CrudRepository<Book,Integer> {
}
2.7ManiController类内容：
package com.example.demo
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.ResponseBody
@Controller
//这个只是为了方便导入测试数据的控制器
public class MainController {
@Autowired
private BookRepository bookRepository
@RequestMapping("/initData")
@ResponseBody
public Iterable<Book> index(){
//导入测试数据
for(int i=1
Book book=new Book()
Author author=new Author()
author.setName("ar "+i)
author.setAge(i*20)
book.setName("bk "+i)
book.setPrice(i*15)
book.setAuthor(author)
bookRepository.save(book)
}
return bookRepository.findAll()
}
}
2.8DemoApplication类内容：
package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
2.9application.properties内容：
spring.jpa.hibernate.ddl-auto=create
spring.datasource.url=jdbc:mysql://localhost:3306/你的数据库
spring.datasource.username=你的数据库账号
spring.datasource.password=你的数据库密码
3.测试
3.1先访问localhost:8080/initData初始化下测试数据，
3.2访问localhost:8080/books 和localhost:8080/authors进行测试，由于前面我们勾选了rest依赖，所以spring自动帮我们生成好了restful 风格的http接口，通过这2个网址可以进行get查询，可以看到查询book的时候book里的author字段也会展示出来.
本文内容由网友自发贡献，版权归原作者所有，本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容，请联系:hwhale#tublm.com(使用前将#替换为@)
