java - 意外查询被Hibernate和JPA触发

我已经编写了用于从数据库获取数据的代码，但是它还会引发意外的查询：

@SuppressWarnings("unchecked")
    @Transactional
    public List<Job> getAppliedPositionsById(Long userId) {
//      String currentDate = SQLDateFormator.getCurrentDateInSqlFormat();
        String strQuery = "from Job x left join x.applications a where a.applicant.id = :userId";
        Query query = entityManager.createQuery(strQuery);
        query.setParameter("userId", userId);
        return query.getResultList();
    }

在return query.getResultList();上触发两个查询。由于第二个查询，我得到了例外。

两个查询

休眠：

    select
        job0_.id as id1_5_0_,
        applicatio1_.id as id1_1_1_,
        job0_.close_date as close_da2_5_0_,
        job0_.committee_chair_id as committe6_5_0_,
        job0_.description as descript3_5_0_,
        job0_.publish_date as publish_4_5_0_,
        job0_.title as title5_5_0_,
        applicatio1_.applicant_id as applican6_1_1_,
        applicatio1_.current_job_institution as current_2_1_1_,
        applicatio1_.current_job_title as current_3_1_1_,
        applicatio1_.current_job_year as current_4_1_1_,
        applicatio1_.cv_id as cv_id7_1_1_,
        applicatio1_.job_id as job_id8_1_1_,
        applicatio1_.research_statement_id as research9_1_1_,
        applicatio1_.submit_date as submit_d5_1_1_,
        applicatio1_.teaching_statement_id as teachin10_1_1_
    from
        jobs job0_
    left outer join
        applications applicatio1_
            on job0_.id=applicatio1_.job_id
    where
        applicatio1_.applicant_id=?

休眠：

    select
        user0_.id as id1_8_0_,
        user0_.address as address2_8_0_,
        user0_.email as email3_8_0_,
        user0_.first_name as first_na4_8_0_,
        user0_.last_name as last_nam5_8_0_,
        user0_.password as password6_8_0_,
        user0_.phone as phone7_8_0_
    from
        users user0_
    where
        user0_.id=?

Users表上的第二个查询完全没有必要。

Job实体

   @Id
    @GeneratedValue
    private Long id;

    private String title;

    private String description;

    @Column(name = "publish_date")
    private Date publishDate;

    @Column(name = "close_date")
    private Date closeDate;

    @ManyToOne
    @JoinColumn(name = "committee_chair_id")
    private User committeeChair;

    @ManyToMany
    @JoinTable(name = "job_committee_members",
        joinColumns = @JoinColumn(name = "job_id") ,
        inverseJoinColumns = @JoinColumn(name = "user_id") )
    @OrderBy("lastName asc")
    private List<User> committeeMembers;

    @OneToMany(mappedBy = "job")
    @OrderBy("date asc")
    private List<Application> applications;
}

Application实体：

 @Id
    @GeneratedValue
    private Long id;

    @ManyToOne
    private Job job;

    @ManyToOne
    private User applicant;

    @Column(name = "submit_date")
    private Date submitDate;

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

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

    @Column(name = "current_job_year")
    private Integer currentJobYear;

    @ElementCollection
    @CollectionTable(name = "application_degrees",
        joinColumns = @JoinColumn(name = "application_id") )
    @OrderBy("year desc")
    private List<Degree> degrees;

    @OneToOne
    private File cv;

    @OneToOne
    @JoinColumn(name = "research_statement_id")
    private File researchStatement;

    @OneToOne
    @JoinColumn(name = "teaching_statement_id")
    private File teachingStatement;

    @OneToMany(mappedBy = "application",
        cascade = { CascadeType.MERGE, CascadeType.PERSIST })
    @OrderColumn(name = "round_index")
    private List<Round> rounds;
}

User实体：

@Id
    @GeneratedValue
    private Long id;

    @Column(unique = true, nullable = false)
    private String email;

    @Column(nullable = false)
    private String password;

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

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

    private String address;

    private String phone;

    @OneToMany(mappedBy = "applicant")
    @OrderBy("id desc")
    private List<Application> applications;
}

最佳答案

根据JPA 2.0规范，默认值如下所示：


  一对多：LAZY
  
  ManyToOne：EAGER
  
  多对多：LAZY
  
  一对一：EAGER


您在Application类中

@ManyToOne
private User applicant;

如果您将其切换为LAZY

@ManyToOne(fetch = FetchType.LAZY)

它应该按照您想要的方式工作。