问题

Question

问题

我定义了两个实体：School和District。一个地区可以有很多学校，学校可以属于一个学区在针对此端点GET执行http://localhost:8080/districts请求时，我希望获得所有区域的列表，而不会获取每个区域的相关学校集。但似乎无论我做什么，hibernate都会调用DB来为每个学校单独获取数据。

实体

学校

@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 = ? 

....

如上所示，SELECT FROM school重复了数百次，尽管将schoolList配置为延迟加载。

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'

Answer 1

在尝试获取所有可用的学校时，看起来您的代码甚至无法使用@JsonIgnore字段district，您应该收到类似的内容：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException：没有为类找到序列化器 org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer而且没有发现创建BeanSerializer的属性（以避免异常，禁用SerializationFeature.FAIL_ON_EMPTY_BEANS）（通过引用链：的java.util.ArrayList [0] - ＆GT; com.mberazouski.stackoverflow.springboothibernate.model.School [＆＃34;区＆＃34;] - ＆GT; com.mberazouski.stackoverflow.springboothibernate.model.District _ _ $$ jvstad5_0 [ ＆＃34;处理＆＃34;]）在 com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from（InvalidDefinitionException.java:77）〜[杰克逊 - 数据绑定-2.9.6.jar：2.9.6]

但是如果你要添加这个注释 - 一切都应该按预期开始工作。所以应该添加的唯一变化应该是：

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "district_id")
@JsonIgnore
private District district;

跟踪结果将是：

2018-06-17 17：27：56.431 DEBUG 25024 --- [nio-8080-exec-1] org.hibernate.SQL：选择school0_.id为 id1_3_，school0_.closed为closed2_3_，school0_.district_id为 district8_3_，school0_.enrollment as enrollme3_3_，school0_.grade_high 作为grade_hi4_3_，school0_.grade_low作为grade_lo5_3_，school0_.name为 name6_3_，school0_.number as number7_3_ from school school0 _

与此相反，如果你要删除懒惰：

@ManyToOne
@JoinColumn(name = "district_id")
private District district;

我们将获得完整的结果：

用于测试的控制器：

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();
    }
}

希望建议的更改能解决您的问题。

祝你好运。

Answer 2

最后想出来了......为了简单起见，我最初发布这个问题并没有包含所有代码。不幸的是，错误的代码不是我最初发布的。

发生了什么

我为School对象创建了Projection，并将投影映射到SchoolRepository，如下面的代码所示。我思想投影仅在REST请求中明确指定时应用（即：/schools?projection=schoolExcerpt）但显然，投影一直在应用。由于某些原因，District对象将SchoolProjection应用于每个相关学校 - ＆gt;即使存在@JsonIgore注释，也会导致SQL查询单独从每个学校获取数据。

我如何解决问题

通过简单地移除投影，我能够检索所有Districts的列表，而无需进行数千次调用来解析每个关联的学校对象。

@RepositoryRestResource(excerptProjection = SchoolProjection.class)  //removing this line solves my problems
public interface SchoolRepository extends CrudRepository<School, Long>{    

}

PS

我实际上甚至不需要@JsonIgnore注释... HATEOAS足够智能，不包含相关对象 - 而是包含指向相关对象的链接。

Answer 3

在您的情况下，您必须为区域服务调用创建另一个VIEW，或者您想尝试@JSONIGNORE schoolList属性以使LazyLoad生效（我猜你的表示层是JSON）。

当你正在进行区域服务调用时，它正在返回带有lazyload ofcourse的District对象，但是一旦你的POJO到JSON转换由控制器处理，它就会调用School getter然后School对象的另一种方法，用于创建完整的数据表示，使hibernate也加载学校对象。

<强>更新

在github中为您添加了示例代码以供参考。

您可以选择以下三个选项：

@JsonIgnore - 将完全忽略任何序列化/反序列化的属性。不确定这是不是你真正想要它。
@JsonManagedReference & @JsonManagedReference - 由于hibernate / table交叉引用结构，将避免json递归/ stackoverflow问题。
@JsonIgnoreProperties - 避免参考实体的json递归问题的另一种方法。

注意：FetchType.LAZY是默认设置，因此未明确说明。

快速参考的代码段：

@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;

}

Spring Data REST HATEOS：不是延迟加载

问题

实体

学校

区

日志输出

3 个答案:

发生了什么

我如何解决问题

PS