为什么 PostPersist 需要设置 oneToOne 子实体的 id？

Question

我正在尝试实现双向 OneToOne 映射并从父实体 (Project.java) 插入子实体 (ProjectDetails.java)。但是，实体管理器试图插入 null 作为子实体 (ProjectDetails) 的 id。

错误日志：

[EL Fine]: sql: 2019-08-19 01:16:50.969--ClientSession(1320691525)--Connection(926343068)--INSERT INTO project (name) VALUES (?)
    bind => [Project]
[EL Fine]: sql: 2019-08-19 01:16:50.973--ClientSession(1320691525)--Connection(926343068)--SELECT @@IDENTITY
[EL Fine]: sql: 2019-08-19 01:16:50.983--ClientSession(1320691525)--Connection(926343068)--INSERT INTO project_details (project_id, details) VALUES (?, ?)
    bind => [null, Details]
[EL Fine]: sql: 2019-08-19 01:16:50.986--ClientSession(1320691525)--SELECT 1
[EL Warning]: 2019-08-19 01:16:50.991--UnitOfWork(1746098804)--Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.7.4.v20190115-ad5b7c6b2a): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: java.sql.SQLIntegrityConstraintViolationException: Column 'project_id' cannot be null
Error Code: 1048

我尝试从@OneToOne 中删除 insertable=false 和 updatable=false，但它给了我错误，同一列不能被引用两次。

我有以下实体 classes。

Class：项目

package com.example.playground.domain.dbo;

import com.example.playground.jsonviews.BasicView;
import com.example.playground.jsonviews.ProjectView;
import com.fasterxml.jackson.annotation.JsonView;
import lombok.Data;
import lombok.ToString;
import org.eclipse.persistence.annotations.JoinFetch;
import org.eclipse.persistence.annotations.JoinFetchType;

import javax.persistence.*;

@JsonView(BasicView.class)
@Data
@Entity
@Table(name = "project")
public class Project {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="project_id")
    private Integer projectId;

    @Column(name="name")
    private String name;

    @ToString.Exclude
    @JsonView(ProjectView.class)
    @OneToOne(mappedBy = "project", cascade = CascadeType.ALL, optional = false)
    private ProjectDetails projectDetails;

}

Class：项目详情

package com.example.playground.domain.dbo;

import com.example.playground.jsonviews.BasicView;
import com.example.playground.jsonviews.ProjectDetailsView;
import com.fasterxml.jackson.annotation.JsonView;
import lombok.Data;
import lombok.ToString;

import javax.persistence.*;

@JsonView(BasicView.class)
@Data
@Entity
@Table(name = "project_details")
public class ProjectDetails {

    @Id
    @Column(name = "project_id")
    private Integer projectId;

    @ToString.Exclude
    @JsonView(ProjectDetailsView.class)
    @OneToOne
    @JoinColumn(name = "project_id", nullable = false, insertable = false, updatable = false)
    private Project project;

    @Column(name = "details")
    private String details;


}

class：项目控制器

package com.example.playground.web;

import com.example.playground.domain.dbo.Project;
import com.example.playground.jsonviews.ProjectView;
import com.example.playground.service.ProjectService;
import com.fasterxml.jackson.annotation.JsonView;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/projects")
public class ProjectController {

    @Autowired
    private ProjectService projectService;

    @GetMapping("/{projectId}")
    @JsonView(ProjectView.class)
    public ResponseEntity<Project> getProject(@PathVariable Integer projectId){
        Project project = projectService.getProject(projectId);
        return ResponseEntity.ok(project);
    }

    @PostMapping
    @JsonView(ProjectView.class)
    public ResponseEntity<Project> createProject(@RequestBody Project projectDTO){
        Project project =  projectService.createProject(projectDTO);
        return ResponseEntity.ok(project);
    }


}

class 项目服务

package com.example.playground.service;

import com.example.playground.domain.dbo.Project;

public interface ProjectService {
    Project createProject(Project projectDTO);

    Project getProject(Integer projectId);
}

class ProjectServiceImpl

package com.example.playground.impl.service;

import com.example.playground.domain.dbo.Project;
import com.example.playground.repository.ProjectRepository;
import com.example.playground.service.ProjectService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class ProjectServiceImpl implements ProjectService {

    @Autowired
    private ProjectRepository projectRepository;

    @Transactional
    @Override
    public Project createProject(Project projectDTO) {
        projectDTO.getProjectDetails().setProject(projectDTO);
        return projectRepository.saveAndFlush(projectDTO);
    }

    @Override
    public Project getProject(Integer projectId) {
        return projectRepository.findById(projectId).get();
    }
}

JPAConfig

package com.example.playground.config;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.annotation.AdviceMode;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.EclipseLinkJpaVendorAdapter;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

@Configuration
@EnableTransactionManagement(mode= AdviceMode.ASPECTJ)
public class JPAConfig{

    @Bean("dataSource")
    @ConfigurationProperties(prefix = "db1")
    public DataSource getDataSource(){
        return DataSourceBuilder.create().build();
    }

    @Bean("entityManagerFactory")
    public LocalContainerEntityManagerFactoryBean getEntityManager(@Qualifier("dataSource") DataSource dataSource){
        EclipseLinkJpaVendorAdapter adapter = new EclipseLinkJpaVendorAdapter();
        LocalContainerEntityManagerFactoryBean em =  new LocalContainerEntityManagerFactoryBean();
        em.setPackagesToScan("com.example.playground.domain.dbo");
        em.setDataSource(dataSource);
        em.setJpaVendorAdapter(adapter);
        em.setPersistenceUnitName("persistenceUnit");
        em.setJpaPropertyMap(getVendorProperties());
        return em;
    }

    @Bean(name = "transactionManager")
    public JpaTransactionManager
    transactionManager(@Qualifier("entityManagerFactory") EntityManagerFactory entityManagerFactory)
    {
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(entityManagerFactory);
        return transactionManager;
    }

    protected Map<String, Object> getVendorProperties()
    {
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("eclipselink.ddl-generation", "none");
        map.put("eclipselink.ddl-generation.output-mode", "database");
        map.put("eclipselink.weaving", "static");
        map.put("eclipselink.logging.level.sql", "FINE");
        map.put("eclipselink.logging.parameters", "true");
        map.put(
                "eclipselink.target-database",
                "org.eclipse.persistence.platform.database.SQLServerPlatform");
        return map;
    }

}

和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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>playground</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Java-Spring-Boot-Playground</name>
    <description>Java playground.</description>

    <properties>
        <java.version>11</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-devtools -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>


        <!-- https://mvnrepository.com/artifact/org.springframework.data/spring-data-jpa -->
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
            <version>2.1.9.RELEASE</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework/spring-aspects -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>

        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>org.eclipse.persistence.jpa</artifactId>
            <version>2.7.4</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.tomcat/tomcat-jdbc -->
        <dependency>
            <groupId>org.apache.tomcat</groupId>
            <artifactId>tomcat-jdbc</artifactId>
            <version>9.0.21</version>
        </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>

        <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>

编辑：可以正常使用，但仍在寻找解释

如果我将以下代码添加到我的项目 class ，它会按预期工作。

  @PostPersist
    public void fillIds(){
        projectDetails.setProjectId(this.projectId);
    }

为什么需要 postPersist？鉴于关系被标记为 oneToOne，JPA 是否应该自动填充这些值？有没有更好的方法？

Answer 1

JPA 按照您的指示执行：您有两个映射到 "project_id"，一个有值，OneToOne 是只读的。这意味着 JPA 必须从您保留为 null 的基本 ID 映射 'projectId' 中提取值，导致它向字段中插入 null。

这是一个常见问题，JPA 中有许多解决方案。首先是将 @ID 映射标记为只读 (insertable/updatable=false) 并让关系映射控制该值。

JPA 2.0 引入了其他解决方案。对于相同的设置，您可以使用 @MapsId 注释标记关系。这告诉 JPA 关系外键值将在指定的 ID 映射中使用，并且会在没有 postPersist 方法的情况下完全按照您预期的那样为您设置它。

JPA 2.0 中的另一种选择是您可以只将 OneToOne 标记为 ID 映射，并从 class 中删除 projectId 属性。显示了一个更复杂的示例 here

为什么 PostPersist 需要设置 oneToOne 子实体的 id？

Why is PostPersist required to set the id of oneToOne child entity?

spring-boot

jpa

eclipselink