Spring Data REST-为什么休眠状态使用FetchType.LAZY获取子实体？

Question

我有一个简单的用例，其中创建了两个实体Account和AccountDetail。

这些实体具有一对一的关系，如下所示：table relationship

Account实体：

@Entity
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@EqualsAndHashCode
public class Account {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String username;

    private String password;

    @OneToOne(mappedBy = "account", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private AccountDetail accountDetail;

}

AccountDetail实体：

@Entity
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Setter
@Getter
@EqualsAndHashCode
public class AccountDetail {
    @Id
    private Long id;

    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL) @MapsId
    private Account account;

    private String firstName;

    private String lastName;
}

我正在使用具有以下依赖项的Spring Boot（v2.3.0）：-Spring Data JPA：使用Hibernate保留实体-其余存储库：通过REST端点公开存储库

问题是即使我指定了AccountDetail，Hibernate仍在获取fetch = FetchType.LAZY实体。

您可以在日志中看到2条sql语句：hibernate log

---

我已经尝试过的：

使用投影：

@Projection(types = {Account.class})
public interface AccountProjection {
    String getUsername();
}

通过以下GET请求http://localhost:8080/accounts/1?projection=accountProjection，我得到：

   {
      "username": "warrior24",
      "_links": {
        "self": {
          "href": "http://localhost:8080/accounts/1"
        },
        "account": {
          "href": "http://localhost:8080/accounts/1{?projection}",
          "templated": true
        },
        "accountDetail": {
          "href": "http://localhost:8080/accounts/1/accountDetail"
        }
      }
    }

不幸的是，使用此解决方案，它仍然会发出2个sql请求。

与@LazyToOne(LazyToOneOption.NO_PROXY)一起使用休眠字节码增强

@OneToOne(mappedBy = "account", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@LazyToOne(LazyToOneOption.NO_PROXY)
private AccountDetail accountDetail;

即使此解决方案也不能解决问题。

结论

我不确定为什么冬眠会拿来孩子。目前，这不是什么大问题，但是如果数据库记录的数量很大，可能会影响性能。

有人有类似的问题，也许知道如何解决吗？

---

更新：包括GET请求的调试日志

2020-05-27 15:23:58.414  INFO 2119 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat-3].[localhost].[/]     : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-05-27 15:23:58.414  INFO 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-05-27 15:23:58.414 DEBUG 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Detected StandardServletMultipartResolver
2020-05-27 15:23:58.415 DEBUG 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : enableLoggingRequestDetails='false': request parameters and headers will be masked to prevent unsafe logging of potentially sensitive data
2020-05-27 15:23:58.415  INFO 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2020-05-27 15:23:58.415 DEBUG 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : GET "/accounts/1", parameters={}
2020-05-27 15:23:58.416 DEBUG 2119 --- [nio-8080-exec-1] o.s.d.r.w.RepositoryRestHandlerMapping   : Mapped to org.springframework.data.rest.webmvc.RepositoryEntityController#getItemResource(RootResourceInformation, Serializable, PersistentEntityResourceAssembler, HttpHeaders)
2020-05-27 15:23:58.416 DEBUG 2119 --- [nio-8080-exec-1] o.j.s.OpenEntityManagerInViewInterceptor : Opening JPA EntityManager in OpenEntityManagerInViewInterceptor
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] stomAnnotationTransactionAttributeSource : Adding transactional method 'findById' with attribute: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Found thread-bound EntityManager [SessionImpl(1137877934<open>)] for JPA transaction
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findById]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] o.s.jdbc.datasource.DataSourceUtils      : Setting JDBC Connection [HikariProxyConnection@646683728 wrapping conn193: url=jdbc:h2:mem:f0df200a-97ea-4e5b-9f80-050ff9a550f7 user=SA] read-only
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@3a65c273]
2020-05-27 15:23:58.417 DEBUG 2119 --- [nio-8080-exec-1] org.hibernate.SQL                        : select account0_.id as id1_0_0_, account0_.password as password2_0_0_, account0_.username as username3_0_0_ from account account0_ where account0_.id=?
2020-05-27 15:23:58.417 TRACE 2119 --- [nio-8080-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [1]
2020-05-27 15:23:58.418 DEBUG 2119 --- [nio-8080-exec-1] org.hibernate.SQL                        : select accountdet0_.account_id as account_3_1_0_, accountdet0_.first_name as first_na1_1_0_, accountdet0_.last_name as last_nam2_1_0_ from account_detail accountdet0_ where accountdet0_.account_id=?
2020-05-27 15:23:58.418 TRACE 2119 --- [nio-8080-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [1]
2020-05-27 15:23:58.418 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Initiating transaction commit
2020-05-27 15:23:58.418 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Committing JPA transaction on EntityManager [SessionImpl(1137877934<open>)]
2020-05-27 15:23:58.418 DEBUG 2119 --- [nio-8080-exec-1] o.s.jdbc.datasource.DataSourceUtils      : Resetting read-only flag of JDBC Connection [HikariProxyConnection@646683728 wrapping conn193: url=jdbc:h2:mem:f0df200a-97ea-4e5b-9f80-050ff9a550f7 user=SA]
2020-05-27 15:23:58.418 DEBUG 2119 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager        : Not closing pre-bound JPA EntityManager after transaction
2020-05-27 15:23:58.421 DEBUG 2119 --- [nio-8080-exec-1] o.s.w.s.m.m.a.HttpEntityMethodProcessor  : Using 'application/hal+json', given [*/*] and supported [application/hal+json]
2020-05-27 15:23:58.421 DEBUG 2119 --- [nio-8080-exec-1] o.s.w.s.m.m.a.HttpEntityMethodProcessor  : Writing [Resource { content: Account(id=1, username=warrior24, password=1234), links: [<http://localhost:8080 (truncated)...]
2020-05-27 15:23:58.421 DEBUG 2119 --- [nio-8080-exec-1] s.d.r.w.j.PersistentEntityJackson2Module : Serializing PersistentEntity org.springframework.data.jpa.mapping.JpaPersistentEntityImpl@45b7be72.
2020-05-27 15:23:58.423 DEBUG 2119 --- [nio-8080-exec-1] .s.ReloadableResourceBundleMessageSource : No properties file found for [classpath:rest-messages] - neither plain properties nor XML
2020-05-27 15:23:58.424 DEBUG 2119 --- [nio-8080-exec-1] .s.ReloadableResourceBundleMessageSource : No properties file found for [classpath:rest-messages_en] - neither plain properties nor XML
2020-05-27 15:23:58.424 DEBUG 2119 --- [nio-8080-exec-1] .s.ReloadableResourceBundleMessageSource : No properties file found for [classpath:rest-messages_en_GB] - neither plain properties nor XML
2020-05-27 15:23:58.426 DEBUG 2119 --- [nio-8080-exec-1] o.j.s.OpenEntityManagerInViewInterceptor : Closing JPA EntityManager in OpenEntityManagerInViewInterceptor
2020-05-27 15:23:58.426 DEBUG 2119 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed 200 OK

Answer 1

尝试使用@JsonIgnore批注，该批注指示基于自省的序列化和反序列化功能将忽略带注释的方法或字段。

@JsonIgnore
@OneToOne(mappedBy = "account", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private AccountDetail accountDetail;

Answer 2

尝试放置@EqualsAndHashCode.Exclude注释以将accountDetail从equals和hashCode方法中排除

@EqualsAndHashCode.Exclude    
 @OneToOne(mappedBy = "account", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
                private AccountDetail accountDetail;

Answer 3

解决方案（种类）

好吧，我想我找到了解决方案，但是很遗憾，它与Spring Data Rest不兼容。

通过添加optional = false，您可以告诉休眠状态，您将确保子引用永远不会为空（在我的情况下为AccountDetail）。

因此，它不需要获取子对象来检查它是否必须创建代理或分配NULL。

@OneToOne(mappedBy = "account", fetch = FetchType.LAZY, cascade = CascadeType.ALL, optional = false)
@LazyToOne(LazyToOneOption.NO_PROXY)
private AccountDetail accountDetail;

此解决方案的问题在于，您无法使用Account批注提供的POST端点来创建新的@RepositoryRestResource资源。由于现在期望AccountDetail不为null，因此需要在JSON中提供此资源的链接（尚不存在）。而且，您无法创建AccountDetail资源，因为它使用帐户表中的外键作为主键。