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我正在使用 Jpa 2.2 和 Hibernate 5.3.7 final jar。以下是测试用例的实体和代码未正确执行：

讲师实体：

@Entity
@DynamicUpdate
@DynamicInsert
   public class Instructor {
        @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    private int id;
    @Version
    @Column(columnDefinition = "int(11) not null default 0")
    private int version = 0;
    **@OneToOne(mappedBy = "instructor", fetch = FetchType.LAZY, orphanRemoval = true, cascade = CascadeType.ALL)
    @JoinColumn(name = "proof_id")
    private IdProof idProof;
    @OneToMany(mappedBy = "instructor", orphanRemoval = true, cascade = CascadeType.ALL)
    private Set<Vehicle> vehicles = new HashSet<>();**

身份证明实体：

@Entity
@Table(name = "id_proof_tbl")
@DynamicInsert
@DynamicUpdate
public class IdProof {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    @Column(updatable = false)
    private int id;
    @Version
    @Column(columnDefinition = "int(11) not null default 0")
    private int version;
    **@OneToOne(fetch = FetchType.LAZY)
    private Instructor instructor;**

车辆实体：

@Entity
@DynamicInsert
@DynamicUpdate
public class Vehicle {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    private int id;
    **@ManyToOne(fetch = FetchType.LAZY)
    private Instructor instructor;**
    **@OneToMany(mappedBy = "vehicle", fetch = FetchType.LAZY, orphanRemoval = true, cascade = CascadeType.ALL)
    private Set<Document> documents = new HashSet<>();**

和文件实体：

@Entity
@DynamicInsert
@DynamicUpdate
public class Document {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    private int id;    
    **@ManyToOne(fetch = FetchType.LAZY)
    private Vehicle vehicle;**

我正在从 MySQL 数据库中获取数据，代码如下所述作为 JUnit 测试：

 @Test
        @Rollback(false)
        @Transactional
        public void fetchPartialDataWithJPQLQueryWithEqualEntityGraph() {

**// Preparing Entity Graph to be passed as a hint .** 

        EntityGraph<Instructor> instructorGraph =   
          em.createEntityGraph(Instructor.class);
            instructorGraph.addAttributeNodes(Instructor_.idProof);
        Subgraph<Vehicle> vehcileSubgraph = 
            instructorGraph.addSubgraph(Instructor_.VEHICLES);
        vehcileSubgraph.addAttributeNodes(Vehicle_.documents);

**//Case 1:**   
        TypedQuery<Instructor> typedQueryJoinFetch = 
        em.createQuery(" select i from Instructor i "
                + " join fetch i.idProof id " 
                + " join fetch i.vehicles v " 
                + " join fetch v.documents vd ",
                Instructor.class);
         typedQueryJoinFetch.setHint("javax.persistence.fetchgraph", 
                                                     instructorGraph);
        List<Instructor> instructors 
                  =typedQueryJoinFetch.getResultList();


**//Case 2:** 
TypedQuery<Instructor> typedQueryLeftJoin = 
   em.createQuery(" select i from Instructor i "
                + " left join i.idProof id "  
                + " left join i.vehicles v " 
                + " left join v.documents vd ",
                Instructor.class);
        typedQueryLeftJoin.setHint("javax.persistence.fetchgraph", 
                                     instructorGraph);
        List<Instructor> instructorsWithLeftJoin = 
                                typedQueryLeftJoin.getResultList();


**// Case 3:**
    try {
        TypedQuery<Instructor> 
        typedQueryLeftJoinAndJoinFetchMixed = 
                   em.createQuery(" select i from Instructor i "
                                + " join fetch i.idProof id " 
                                + " left join i.vehicles v " 
                                + " join fetch v.documents vd ",
                                Instructor.class);
        typedQueryLeftJoinAndJoinFetchMixed.
           setHint("javax.persistence.fetchgraph", instructorGraph);
        List<Instructor> 
              instructorsWithLeftJoinAndJoinFetchMixed = 
                       typedQueryLeftJoinAndJoinFetchMixed
                                .getResultList();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }

                }


**Case 1 executes correctly and results in the inner join between the four 
         tables with below query:** 
    select
            instructor0_.id as id1_2_0_,
            idproof1_.id as id1_1_1_,
            vehicles2_.id as id1_5_2_,
            documents3_.id as id1_0_3_,
            instructor0_.address as address2_2_0_,
            instructor0_.birth_date_time as birth_da3_2_0_,
            instructor0_.birth_date_time_zone_offset as birth_da4_2_0_,
            instructor0_.created_date as created_5_2_0_,
            instructor0_.day_off_time as day_off_6_2_0_,
            instructor0_.day_start_time as day_star7_2_0_,
            instructor0_.father_name as father_n8_2_0_,
            instructor0_.mother_name as mother_n9_2_0_,
            instructor0_.name as name10_2_0_,
            instructor0_.photo as photo11_2_0_,
            instructor0_.monthly_salary as monthly12_2_0_,
            instructor0_.updated_date as updated13_2_0_,
            instructor0_.version as version14_2_0_,
            idproof1_.address as address2_1_1_,
            idproof1_.created_date as created_3_1_1_,
            idproof1_.father_name as father_n4_1_1_,
            idproof1_.instructor_id as instruc12_1_1_,
            idproof1_.is_foreigner as is_forei5_1_1_,
            idproof1_.mother_name as mother_n6_1_1_,
            idproof1_.name as name7_1_1_,
            idproof1_.proof_sequence_no as proof_se8_1_1_,
            idproof1_.sex as sex9_1_1_,
            idproof1_.updated_date as updated10_1_1_,
            idproof1_.version as version11_1_1_,
            vehicles2_.creation_date as creation2_5_2_,
            vehicles2_.instructor_id as instruct8_5_2_,
            vehicles2_.purchased_date_time as purchase3_5_2_,
            vehicles2_.purchased_date_zone_offset as purchase4_5_2_,
            vehicles2_.student_id as student_9_5_2_,
            vehicles2_.updated_date as updated_5_5_2_,
            vehicles2_.vechicle_type as vechicle6_5_2_,
            vehicles2_.vehicle_number as vehicle_7_5_2_,
            vehicles2_.instructor_id as instruct8_5_0__,
            vehicles2_.id as id1_5_0__,
            documents3_.name as name2_0_3_,
            documents3_.vehicle_id as vehicle_3_0_3_,
            documents3_.vehicle_id as vehicle_3_0_1__,
            documents3_.id as id1_0_1__ 
        from
            instructor instructor0_ 
        inner join
            id_proof_tbl idproof1_ 
                on instructor0_.id=idproof1_.instructor_id 
        inner join
            vehicle vehicles2_ 
                on instructor0_.id=vehicles2_.instructor_id 
        inner join
            document documents3_ 
                on vehicles2_.id=documents3_.vehicle_id

**Case 2 executes successfully and results in left outer join between 
four tables with below query:** 
  select
        instructor0_.id as id1_2_0_,
        idproof1_.id as id1_1_1_,
        vehicles2_.id as id1_5_2_,
        documents3_.id as id1_0_3_,
        instructor0_.address as address2_2_0_,
        instructor0_.birth_date_time as birth_da3_2_0_,
        instructor0_.birth_date_time_zone_offset as birth_da4_2_0_,
        instructor0_.created_date as created_5_2_0_,
        instructor0_.day_off_time as day_off_6_2_0_,
        instructor0_.day_start_time as day_star7_2_0_,
        instructor0_.father_name as father_n8_2_0_,
        instructor0_.mother_name as mother_n9_2_0_,
        instructor0_.name as name10_2_0_,
        instructor0_.photo as photo11_2_0_,
        instructor0_.monthly_salary as monthly12_2_0_,
        instructor0_.updated_date as updated13_2_0_,
        instructor0_.version as version14_2_0_,
        idproof1_.address as address2_1_1_,
        idproof1_.created_date as created_3_1_1_,
        idproof1_.father_name as father_n4_1_1_,
        idproof1_.instructor_id as instruc12_1_1_,
        idproof1_.is_foreigner as is_forei5_1_1_,
        idproof1_.mother_name as mother_n6_1_1_,
        idproof1_.name as name7_1_1_,
        idproof1_.proof_sequence_no as proof_se8_1_1_,
        idproof1_.sex as sex9_1_1_,
        idproof1_.updated_date as updated10_1_1_,
        idproof1_.version as version11_1_1_,
        vehicles2_.creation_date as creation2_5_2_,
        vehicles2_.instructor_id as instruct8_5_2_,
        vehicles2_.purchased_date_time as purchase3_5_2_,
        vehicles2_.purchased_date_zone_offset as purchase4_5_2_,
        vehicles2_.student_id as student_9_5_2_,
        vehicles2_.updated_date as updated_5_5_2_,
        vehicles2_.vechicle_type as vechicle6_5_2_,
        vehicles2_.vehicle_number as vehicle_7_5_2_,
        vehicles2_.instructor_id as instruct8_5_0__,
        vehicles2_.id as id1_5_0__,
        documents3_.name as name2_0_3_,
        documents3_.vehicle_id as vehicle_3_0_3_,
        documents3_.vehicle_id as vehicle_3_0_1__,
        documents3_.id as id1_0_1__ 
    from
        instructor instructor0_ 
    left outer join
        id_proof_tbl idproof1_ 
            on instructor0_.id=idproof1_.instructor_id 
    left outer join
        vehicle vehicles2_ 
            on instructor0_.id=vehicles2_.instructor_id 
    left outer join
        document documents3_ 
            on vehicles2_.id=documents3_.vehicle_id

但我只想获取那些在数据库中存在 IdProofs 的教师以及他们在数据库中存在文档的唯一车辆。所以我编写了案例 3​​。但案例 3 导致以下异常： 

 java.lang.IllegalArgumentException: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=vd,role=com.katariasoft.technologies.jpaHibernate.college.data.entity.Vehicle.documents,tableName=document,tableAlias=documents3_,origin=vehicle vehicles2_,columns={vehicles2_.id ,className=com.katariasoft.technologies.jpaHibernate.college.data.entity.utils.Document}}] [ select i from com.katariasoft.technologies.jpaHibernate.college.data.entity.Instructor i  join fetch i.idProof id left join i.vehicles v  join fetch v.documents vd ]

请让我知道如何满足我的案例 3 要求，以获取在 DB 中存在 IdProofs 的所有讲师以及在 DB 中存在文档的唯一车辆。

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2 回答 2

1

您将需要加入文档，而不会fetch因为休眠尝试使用该关键字为不存在的车辆获取这些内容。

   em.createQuery(" select i from Instructor i "
            + " join fetch i.idProof id " 
            + "left join i.vehicles v " 
            + " join v.documents vd ",
            Instructor.class);

现在，在您获得结果之后，在处理/访问车辆文件之前，您只需检查是否Instructor.vehicles为空，如果为真则不继续。

于 2019-01-23T08:55:19.267 回答
0 
  Below code fetches Only those instrcutors having IdProof present in
  DB . If No Instructor is having idProof present in db then written
  query will return empty List as there is inner join between
  Instructor and IdProof . 

  All Instructors not having any vehicle will also be fetched and their
  vehicle list  will be initialised as empty.

  All vehicle not having any document will also be fetched along with
  vehicles having atleast one document . Vehicles not having any
  document can be avoided in code while processing data . 

  But if inner join is created between Vehicle and document and if
  there is no  document present in db then it will make the complete
  result empty . As final inner join will be applied on join results
  evaluted till yet in db on first three tables Instructor , IdProof and 
  Vehcile.


    try {
       TypedQuery<Instructor> 
       typedQueryLeftJoinAndJoinFetchMixed = 
       em.createQuery(" select i from Instructor i "
               + " join fetch i.idProof id " 
               + " left join i.vehicles v " 
               + " left join v.documents vd ",
                    Instructor.class);
       typedQueryLeftJoinAndJoinFetchMixed.
                   setHint("javax.persistence.fetchgraph", instructorGraph);
       List<Instructor> 
           instructorsWithLeftJoinAndJoinFetchMixed = 
                               typedQueryLeftJoinAndJoinFetchMixed
                                        .getResultList();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }

                        }
于 2019-01-24T09:26:29.433 回答