问题描述
我定义了两个实体:学校和区.一个地区可以有很多学校，而一所学校可以属于一个地区.
在对此端点 http://localhost:8080/districts 执行 GET 请求时，我想获取所有学区的列表，而无需获取每个学区的关联学校集.但这似乎不管我做什么，休眠方式都是通过数据库调用来分别获取每个学校的数据.
I have two entities defined: School and District. A district can have many schools and a school can belong to one district.
When executing a GET request against this endpoint http://localhost:8080/districts I would like to get a list of all the districts WITHOUT fetching each district's set of associated schools. But it seems like no matter what I do, hibernate is making DB calls to fetch data for each school individually.
@Getter
@Setter
@NoArgsConstructor
@Entity
public class School {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@NotNull
@Column(unique=true)
private Long number;
@NotNull
@Column
private String name;
@NotNull
private boolean closed;
@Embedded
private ContactInfo contactInfo;
private String gradeLow;
private String gradeHigh;
private int enrollment;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "district_id")
private District district;
}
区
@Getter
@Setter
@NoArgsConstructor
@Entity
public class District {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Column(unique = true)
private Integer number;
private String name;
private String type;
private int enrollment;
private Date updated;
@Embedded
private ContactInfo contactInfo;
@Getter(AccessLevel.NONE)
@JsonIgnore
@OneToMany(fetch = FetchType.LAZY, mappedBy = "district")
private Set<School> schoolList;
}
日志输出
SELECT district0_.id AS id1_5_,
district0_.city AS city2_5_,
district0_.email AS email3_5_,
district0_.fax AS fax4_5_,
district0_.first_name AS first_na5_5_,
district0_.last_name AS last_nam6_5_,
district0_.name_prefix AS name_pre7_5_,
district0_.phone AS phone8_5_,
district0_.state AS state9_5_,
district0_.street AS street10_5_,
district0_.title AS title11_5_,
district0_.website AS website12_5_,
district0_.zip AS zip13_5_,
district0_.enrollment AS enrollm14_5_,
district0_.NAME AS name15_5_,
district0_.number AS number16_5_,
district0_.type AS type17_5_,
district0_.updated AS updated18_5_
FROM district district0_
SELECT schoollist0_.district_id AS distric20_7_0_,
schoollist0_.id AS id1_7_0_,
schoollist0_.id AS id1_7_1_,
schoollist0_.closed AS closed2_7_1_,
schoollist0_.city AS city3_7_1_,
schoollist0_.email AS email4_7_1_,
schoollist0_.fax AS fax5_7_1_,
schoollist0_.first_name AS first_na6_7_1_,
schoollist0_.last_name AS last_nam7_7_1_,
schoollist0_.name_prefix AS name_pre8_7_1_,
schoollist0_.phone AS phone9_7_1_,
schoollist0_.state AS state10_7_1_,
schoollist0_.street AS street11_7_1_,
schoollist0_.title AS title12_7_1_,
schoollist0_.website AS website13_7_1_,
schoollist0_.zip AS zip14_7_1_,
schoollist0_.district_id AS distric20_7_1_,
schoollist0_.enrollment AS enrollm15_7_1_,
schoollist0_.grade_high AS grade_h16_7_1_,
schoollist0_.grade_low AS grade_l17_7_1_,
schoollist0_.NAME AS name18_7_1_,
schoollist0_.number AS number19_7_1_
FROM school schoollist0_
WHERE schoollist0_.district_id = ?
SELECT schoollist0_.district_id AS distric20_7_0_,
schoollist0_.id AS id1_7_0_,
schoollist0_.id AS id1_7_1_,
schoollist0_.closed AS closed2_7_1_,
schoollist0_.city AS city3_7_1_,
schoollist0_.email AS email4_7_1_,
schoollist0_.fax AS fax5_7_1_,
schoollist0_.first_name AS first_na6_7_1_,
schoollist0_.last_name AS last_nam7_7_1_,
schoollist0_.name_prefix AS name_pre8_7_1_,
schoollist0_.phone AS phone9_7_1_,
schoollist0_.state AS state10_7_1_,
schoollist0_.street AS street11_7_1_,
schoollist0_.title AS title12_7_1_,
schoollist0_.website AS website13_7_1_,
schoollist0_.zip AS zip14_7_1_,
schoollist0_.district_id AS distric20_7_1_,
schoollist0_.enrollment AS enrollm15_7_1_,
schoollist0_.grade_high AS grade_h16_7_1_,
schoollist0_.grade_low AS grade_l17_7_1_,
schoollist0_.NAME AS name18_7_1_,
schoollist0_.number AS number19_7_1_
FROM school schoollist0_
WHERE schoollist0_.district_id = ?
SELECT schoollist0_.district_id AS distric20_7_0_,
schoollist0_.id AS id1_7_0_,
schoollist0_.id AS id1_7_1_,
schoollist0_.closed AS closed2_7_1_,
schoollist0_.city AS city3_7_1_,
schoollist0_.email AS email4_7_1_,
schoollist0_.fax AS fax5_7_1_,
schoollist0_.first_name AS first_na6_7_1_,
schoollist0_.last_name AS last_nam7_7_1_,
schoollist0_.name_prefix AS name_pre8_7_1_,
schoollist0_.phone AS phone9_7_1_,
schoollist0_.state AS state10_7_1_,
schoollist0_.street AS street11_7_1_,
schoollist0_.title AS title12_7_1_,
schoollist0_.website AS website13_7_1_,
schoollist0_.zip AS zip14_7_1_,
schoollist0_.district_id AS distric20_7_1_,
schoollist0_.enrollment AS enrollm15_7_1_,
schoollist0_.grade_high AS grade_h16_7_1_,
schoollist0_.grade_low AS grade_l17_7_1_,
schoollist0_.NAME AS name18_7_1_,
schoollist0_.number AS number19_7_1_
FROM school schoollist0_
WHERE schoollist0_.district_id = ?
SELECT schoollist0_.district_id AS distric20_7_0_,
schoollist0_.id AS id1_7_0_,
schoollist0_.id AS id1_7_1_,
schoollist0_.closed AS closed2_7_1_,
schoollist0_.city AS city3_7_1_,
schoollist0_.email AS email4_7_1_,
schoollist0_.fax AS fax5_7_1_,
schoollist0_.first_name AS first_na6_7_1_,
schoollist0_.last_name AS last_nam7_7_1_,
schoollist0_.name_prefix AS name_pre8_7_1_,
schoollist0_.phone AS phone9_7_1_,
schoollist0_.state AS state10_7_1_,
schoollist0_.street AS street11_7_1_,
schoollist0_.title AS title12_7_1_,
schoollist0_.website AS website13_7_1_,
schoollist0_.zip AS zip14_7_1_,
schoollist0_.district_id AS distric20_7_1_,
schoollist0_.enrollment AS enrollm15_7_1_,
schoollist0_.grade_high AS grade_h16_7_1_,
schoollist0_.grade_low AS grade_l17_7_1_,
schoollist0_.NAME AS name18_7_1_,
schoollist0_.number AS number19_7_1_
FROM school schoollist0_
WHERE schoollist0_.district_id = ?
....
如上所述，尽管将schoolList配置为延迟加载，但 SELECT FROM school 却重复了数百次.
The SELECT FROM school as seen above, repeats hundreds of times despite having the schoolList configured as a lazy load.
版本:
springBootVersion = '1.4.2.RELEASE'
hibernate-core:5.0.11
'org.springframework.boot:spring-boot-starter-data-jpa'
'org.springframework.boot:spring-boot-starter-data-rest'
'org.springframework.boot:spring-boot-starter-web'
'org.springframework.boot:spring-boot-starter-actuator'
'org.springframework.boot:spring-boot-starter-hateoas'
'org.springframework.boot:spring-boot-starter-security'
推荐答案
最后想出了这一点...为了简单起见，当我最初发布此问题时，我并未包括所有代码.不幸的是，错误的代码并不是我最初发布的.
Finally figured this out ... I didn't include all of the code when I originally posted this question for simplicity sake. Unfortunately, the erroneous code was not something I originally posted.
我创建了一个 Projection 作为我的 School 对象，并将投影映射到 SchoolRepository ，如下面的代码所示.我认为仅在REST请求中明确指定投影时才应用投影(即:/schools?projection = schoolExcerpt )，但是显然，投影一直在被应用.出于某种原因， District 对象将 SchoolProjection 应用于每个关联的学校->导致SQL查询以单独的方式从每个学校获取数据，即使使用 @存在JsonIgore 批注.
I had created a Projection for my School object and mapped the projection to the SchoolRepository as shown in the below code. I thought the projection was only applied when explicitly specified in a REST request (ie : /schools?projection=schoolExcerpt) But apparently, the projection was getting applied all the time. And for some reason, the District object was applying the SchoolProjection to each associated school -> resulting in SQL queries to fetch data form each school individually even with the @JsonIgore annotation present.
通过简单地删除投影，我能够检索所有 Districts 的列表，而无需进行数千次调用来解决每个关联的学校对象.
By simply removing the projection I was able to retrieve a list of all Districts without making thousands of calls to resolve each associated school object.
@RepositoryRestResource(excerptProjection = SchoolProjection.class) //removing this line solves my problems
public interface SchoolRepository extends CrudRepository<School, Long>{
}
PS
实际上我什至不需要 @JsonIgnore 批注... HATEOAS非常聪明，不包含相关对象-而是包含了指向相关对象的链接.
PS
I don't actually even need the @JsonIgnore annotation... HATEOAS is smart enough to not include related objects - instead it includes links to related objects.
这篇关于Spring Data REST HATEOS:不是延迟加载的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！