问题
Problem
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.
Entities
School
@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;
}
District
@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;
}
Log Output
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 = ?
....
The SELECT FROM school as seen above, repeats hundreds of times despite having the schoolList configured as a lazy load.
Versions:
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'
回答1:
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.
What Was Happening
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.
How I Solved the Issue
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
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.
回答2:
Looks like your code even not workable, without @JsonIgnore for the field district during attempt to get all available schools you should recieve something like that:
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]->com.mberazouski.stackoverflow.springboothibernate.model.School["district"]->com.mberazouski.stackoverflow.springboothibernate.model.District_$$_jvstad5_0["handler"]) at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77) ~[jackson-databind-2.9.6.jar:2.9.6]
But if you will add this annotation - everything should start working as expected. So the only change which should be added should be:
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "district_id")
@JsonIgnore
private District district;
The result of trace will be:
2018-06-17 17:27:56.431 DEBUG 25024 --- [nio-8080-exec-1] org.hibernate.SQL : select school0_.id as id1_3_, school0_.closed as closed2_3_, school0_.district_id as district8_3_, school0_.enrollment as enrollme3_3_, school0_.grade_high as grade_hi4_3_, school0_.grade_low as grade_lo5_3_, school0_.name as name6_3_, school0_.number as number7_3_ from school school0_
In opposite to that if you will remove lazy:
@ManyToOne
@JoinColumn(name = "district_id")
private District district;
We will get full result:
Controller which was used for the test:
import com.mberazouski.stackoverflow.springboothibernate.model.School;
import com.mberazouski.stackoverflow.springboothibernate.repository.SchoolRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.List;
@RestController
public class SchoolController {
@Autowired
SchoolRepository schoolRepository;
@GetMapping("/schools")
public List<School> getAllSchools() {
return schoolRepository.findAll();
}
}
Hope that suggested change will solve your issue.
Good luck.
回答3:
In your case, you either have to create another VIEW for districts service call or you wanna try the @JSONIGNORE for schoolListproperty to have LazyLoad in effect (I am guessing your presentation layer is JSON).
What's happening is, when you are making a districts service call, its returning the District object with lazyload ofcourse, but as soon as your POJO to JSON transformation is handled by controller, it is calling School getter and then further method of School object to create full data representation causing hibernate to load school objects as well.
UPDATE
Added sample code for you in github to refer.
You can choose between three options:
@JsonIgnore- will completely ignore the property for any serialization/deserialization. Not sure if that's what you really want it.@JsonManagedReference & @JsonManagedReference- will avoid json recursion/stackoverflow issue due to hibernate/table cross referencial structure.@JsonIgnoreProperties- another way to avoid json recursion issue for referencial entities.
NOTE: FetchType.LAZY is by default, so haven't explicitly stated it.
Code snippet for quick reference:
@Getter
@Setter
@Entity
public class District {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
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;
@OneToMany(mappedBy = "district")
//@JsonManagedReference //to avoid JSON recursion solution 1
//@JsonIgnoreProperties("district") //to avoid JSON recursion solution 2
@JsonIgnore
private Set<School> schools;
}
@Getter
@Setter
@Entity
public class School {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(unique=true, nullable = false)
private Long number;
@Column(nullable = false)
private String name;
private boolean closed;
@Embedded
private ContactInfo contactInfo;
private String gradeLow;
private String gradeHigh;
private int enrollment;
@ManyToOne
@JoinColumn(name = "district_id", nullable = false)
//@JsonBackReference //to avoid JSON recursion solution 1
//@JsonIgnoreProperties("schools") //to avoid JSON recursion solution 2
@JsonIgnore
private District district;
}
来源：https://stackoverflow.com/questions/50891296/spring-data-rest-hateos-not-lazy-loading