SpringBoot-JPA进行多表连接查询

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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

这里写图片描述

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/> <!-- lookup parent from repository -->    </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;@Entitypublic class Author {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private int Id;    private String name;    private int age;    @OneToMany( mappedBy = "author" )//作者与书 是一对多的关系，mappedBy 指的是通过  book表中的author字段来映射，mappedBy一般用来设置为关联表的外键字段，这里Book实体中的外键字段为author，则设置为author,设置为别的字段没法进行连接查询    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.*;@Entitypublic class Book {    @javax.persistence.Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private int Id;    private String name;    private float price;    @JoinColumn    @ManyToOne(cascade = CascadeType.ALL)    //book与作者是多对一的关系，JoinColumn用来加入外键，Cacade 用来级联，CascadeType.Remove 指级联删除，被关联表元祖删除，关联表的对应元祖也会被删除，这里book是关联表，通过外键字段author(在数据库中为author_id外键）关联author表，author是被关联表    // 同样 CascadeType.Persist则是级联存储，其他几个 对应他们的本身单词意思    //CascadType.ALL 则包含了所有级联操作    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;i<10;++i){            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;@SpringBootApplicationpublic class DemoApplication {    public static void main(String[] args) {        SpringApplication.run(DemoApplication.class, args);    }}

2.9application.properties内容：

spring.jpa.hibernate.ddl-auto=createspring.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.

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