我正在将Jpa 2.2与Hibernate 5.3.7 final jar一起使用。以下是我的实体 和测试用例代码无法正确执行：
教师实体：
charIdProof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<>();**
车辆实体：
@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;**
和文档实体：
@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<>();**
我正在从mysql数据库中获取数据，其代码如下所示： JUnit测试：
@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;**
但是我只想获取那些在其中存在IdProofs的讲师 数据库及其仅有的文件中存在文件的车辆 数据库。因此，我对情况3进行了编码。但是情况3导致执行力降低：
@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 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
请让我知道如何满足我的案例3要求 db中存在IdProofs的所有讲师以及db中存在文档的唯一载具。
答案 0 :(得分：1)
您需要在没有fetch的情况下加入文档，因为休眠状态正试图使用该关键字为不存在的车辆获取这些文件。
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，在获得结果之后，在处理/访问车辆文档之前，您只需检查Instructor.vehicles是否为空，如果为true，就不会继续。
答案 1 :(得分：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();
}
}