如何在Spring Data JPA中应用本机联接查询？

问题描述

这是我的实体类。

JobPost.java

@Entity
@Table(name = "job_post")
public class JobPost {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "job_post_id")
    private Long jobPostId;

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

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

    @Column(name = "vacancy")
    private int vacancy;

    @Column(name = "posted_date")
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date postedDate;

    @Column(name = "total_applicants")
    private int totalApplicants;
    
}

JobApplication.java

@Entity
@Table(name = "job_application")
public class JobApplication {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "job_application_id")
    private Long jobApplicationId;

    @Column(name = "job_post_id")
    private Long jobPostId;

    @Column(name = "applicant_id")
    private Long applicantId;
}

Applicant.java

@Entity
@Table(name = "applicant")
public class Applicant {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "applicant_id")
    private Long applicantId;

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

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

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

}

我的主要目标是在 JobPostId 上列出 ApplicantList 。我对Spring数据JPA完全陌生。 JPA映射正确吗？我不知道我应该触发哪个查询才能获取基于jobPostId的applicistList。

解决方法

我建议使用JpaMappings并使用SpringData而不是使用本机查询。 遵循的步骤： 多对多：

使用JoinTable直接映射JobPost和Applicant，而不创建单独的类。

帮助链接： https://attacomsian.com/blog/spring-data-jpa-many-to-many-mapping

使用SpringData JPA findOne或findById方法（取决于Spring版本）。如果您使用EAGER fetch，则它将为您提供与JobPost ID相关的所有申请人。

一对多

保留JobApplication类并使用OneToMany注释。

帮助链接： https://attacomsian.com/blog/spring-data-jpa-one-to-many-mapping

查询：

@Query("select a from JobPost j inner join j.jobApplicantList ja inner join ja.applicant a where j.jobPostId=:jobPostId")
    List<String> findAllJobApplicants(@Param("jobPostId") Long jobPostId);

,

我认为您应该以这种方式配置映射。为此，您只需要两个实体 JobPost.java

    @Entity
    @Table(name = "job_post")
    public class JobPost {
    
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;
    
        @Column(name = "job_title")
        private String jobTitle;
    
        @Column(name = "job_description")
        private String jobDescription;
    
        @Column(name = "vacancy")
        private int vacancy;
    
        @Column(name = "posted_date")
        @JsonFormat(pattern = "yyyy-MM-dd")
        private Date postedDate;
    
        @Column(name = "total_applicants")
        private int totalApplicants;
    
        @ManyToMany
        @JoinTable(name = "applicant_job_post",joinColumns = {
                        @JoinColumn(name = "job_post_id",referencedColumnName = "id")
                },inverseJoinColumns = {
                @JoinColumn(name = "applicant_id",referencedColumnName = "id")
        })
        private Set<Applicant> applicants;
    
        public JobPost() {
        }
    
        public void addApplicant(Applicant applicant) {
            applicants.add(applicant);
            applicant.getJobPosts().add(this);
        }
    
        public void removeApplicant(Applicant applicant) {
            applicants.remove(applicant);
            applicant.getJobPosts().remove(this);
        }
   }

Applicant.java

@Entity
@Table(name = "applicant")
public class Applicant {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

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

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

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

    @ManyToMany(mappedBy = "applicants")
    private Set<JobPost> jobPosts;

    public Applicant() {
    }

    public void addJobPost(JobPost jobPost) {
        jobPosts.add(jobPost);
        jobPost.getApplicants().add(this);
    }

    public void removeJobPost(JobPost jobPost) {
        jobPosts.remove(jobPost);
        jobPost.getApplicants().remove(this);
    }
}