【Spring Boot JPA】ManyToOne OneToMany学习笔记

Spring Data JPA的官方文档参考：https://docs.spring.io/spring-data/jpa/docs/current/reference/html/

我希望使用JPA进行两个表的一对多和多对一的关系：

相册（Album）1 : N 相片（Photo）

Album的定义为：

import com.fasterxml.jackson.annotation.JsonManagedReference;
import lombok.Data;

import javax.persistence.*;
import java.util.List;

@Entity
@Table(name = "t_album")
@Data
public class Album {
    @Id
    private String id;
    @Column
    private String name;
    @JsonManagedReference
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "album")
    private List<Photo> photos;
}

Photo的定义为：

import com.fasterxml.jackson.annotation.JsonBackReference;
import lombok.Data;

import javax.persistence.*;

@Entity
@Table(name = "t_photo")
@Data
public class Photo {
    @Id
    private String id;
    @Column
    private String name;
    @JsonBackReference
    @ManyToOne(cascade = CascadeType.REFRESH)
    @JoinColumn(name="album_id", referencedColumnName = "id")
    private Album album;
}

说明：

jackson中的@JsonBackReference和@JsonManagedReference，以及@JsonIgnore均是为了解决对象中存在双向引用导致的无限递归（infinite recursion）问题。这些标注均可用在属性或对应的get、set方法中。  
@JsonBackReference和@JsonManagedReference：这两个标注通常配对使用，通常用在父子关系中。@JsonBackReference标注的属性在序列化（serialization，即将对象转换为json数据）时，会被忽略（即结果中的json数据不包含该属性的内容）。@JsonManagedReference标注的属性则会被序列化。在序列化时，@JsonBackReference的作用相当于@JsonIgnore，此时可以没有@JsonManagedReference。但在反序列化（deserialization，即json数据转换为对象）时，如果没有@JsonManagedReference，则不会自动注入@JsonBackReference标注的属性（被忽略的父或子）；如果有@JsonManagedReference，则会自动注入自动注入@JsonBackReference标注的属性。  
@JsonIgnore：直接忽略某个属性，以断开无限递归，序列化或反序列化均忽略。当然如果标注在get、set方法中，则可以分开控制，序列化对应的是get方法，反序列化对应的是set方法。在父子关系中，当反序列化时，@JsonIgnore不会自动注入被忽略的属性值（父或子），这是它跟@JsonBackReference和@JsonManagedReference最大的区别。

Album的Repository定义：

import com.example.jpa.model.Album;
import org.springframework.data.jpa.repository.JpaRepository;

public interface AlbumRepository extends JpaRepository<Album, String> {
}

Photo的Repository定义：

import com.example.jpa.model.Album;
import com.example.jpa.model.Photo;
import org.springframework.data.jpa.repository.JpaRepository;

import java.util.List;

public interface PhotoRepository extends JpaRepository<Photo, String> {
    public List<Photo> findByAlbum(Album album);
}

说明：findByAlbum是希望获取一个相册中所有的照片

Album的Restful服务：

import com.example.jpa.model.Album;
import com.example.jpa.model.Photo;
import com.example.jpa.repository.AlbumRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Example;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;
import java.util.Optional;

@RestController
public class AlbumService {
    @Autowired
    AlbumRepository albumRepository;

    @RequestMapping(value = "/album", method = RequestMethod.POST)
    public Album addAlbum(@RequestBody Album album) {
        return albumRepository.save(album);
    }

    @RequestMapping(value = "/album", method = RequestMethod.GET)
    public List<Album> getAllAlbum() {
        return albumRepository.findAll();
    }

    @RequestMapping(value = "/album/photo", method = RequestMethod.GET)
    public List<Photo> getAlbumPhoto(@RequestBody Album album) {
        Optional<Album> optional = albumRepository.findOne(Example.of(album));
        return optional.get().getPhotos();
    }
}

Photo的Restful服务：

import com.example.jpa.model.Album;
import com.example.jpa.model.Photo;
import com.example.jpa.repository.PhotoRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
public class PhotoService {
    @Autowired
    PhotoRepository photoRepository;

    @RequestMapping(value = "/photo", method = RequestMethod.POST)
    public Photo addPhoto(@RequestBody Photo photo) {
        return  photoRepository.save(photo);
    }

    @RequestMapping(value = "/photo/all", method = RequestMethod.GET)
    public List<Photo> getAllPhotos() {
        return photoRepository.findAll();
    }

    @RequestMapping(value = "/photo/album", method = RequestMethod.GET)
    public List<Photo> getAlbumPhotos(@RequestBody Album album) {
        return photoRepository.findByAlbum(album);
    }
}

pom文件定义为：

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.8.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>jpa</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>jpa</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <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-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.8</version>
            <scope>provided</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.60</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

application.properties配置文件：

#配置数据库连接地址
spring.datasource.primary.jdbc-url=jdbc:h2:mem:testdb
#;AUTO_SERVER=TRUE;DB_CLOSE_ON_EXIT=TRUE
#配置数据库驱动
spring.datasource.primary.driver-class-name=org.h2.Driver
#配置数据库用户名
spring.datasource.primary.username=sa
#配置数据库密码
spring.datasource.primary.password=
#配置能远程访问
spring.h2.console.settings.web-allow-others=true
#配置访问地址
spring.h2.console.path=/h2-console
#配置项目启动 h2就启动
spring.h2.console.enabled=true

现在启动服务，使用PostMan进行测试：

添加Album:

POST: http://127.0.0.1:8080/album

Body:

{
    "id":"album1",
    "name":"the album1"
}

添加Photo:

POST: http://127.0.0.1:8080/photo

Body:

{
    "id":"photo1",
    "name":"the photo1",
    "album":{
        "id":"album1"
    }
}

查询Album中的Photo:

GET: http://127.0.0.1:8080/album/photo

Body:

{
    "id":"album1"
}