java - Spring Boot 获取惰性 - 无法写入 JSON : could not initialize proxy - no Session

Question

首先，我知道有几个带有解决方案的线程，但我不理解它们，而且它们似乎根本没有帮助我。我知道问题出在哪里了。由于 session 已关闭而导致懒惰。我认为 @Transactional 会有帮助，但事实并非如此。而且我知道我不应该在 Controller 中使用注释。当我解决这个问题后我会改变它。我还将创建一个 DTO，而不是注释实体。

我得到了我的实体 MlpConfig，我想将所有配置发送到我的前端。但与其他实体的联系会带来这个问题:

Could not write JSON: could not initialize proxy [com.project.data.ActivationFunction#4] - no Session; nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy...

我需要响应中的所有信息(ActivationFunction、图层)，但我真的不想获取 EAGER。即使我在 MlpConfig 中将其设置为 EAGER，ActivationFunction 也会提示同样的问题(导致连接到 MlpConfig)

实体MlpConfig(在响应有效的所有外部对象上使用@JsonIgnore):

@Entity
@Data
@NoArgsConstructor
public class MlpConfig {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @NotBlank(message = "Name for the MlpConfig is required")
    @Column(name = "name", nullable = false, length = 255)
    private String name;

    private String description;

    @NotNull(message = "Batch Size is required")
    private int batchSize;

    @NotNull(message = "Epoch Number is required")
    private int epochNumber;

    @EqualsAndHashCode.Exclude
    @ToString.Exclude
    @ManyToOne(fetch = FetchType.LAZY)
    private ActivationFunction activationFunction;

    @JsonIgnore
    @OneToMany(mappedBy = "mlpConfig", orphanRemoval = true)
    private Set<Layer> layers = new HashSet<>();

    @JsonIgnore
    @EqualsAndHashCode.Exclude
    @ToString.Exclude
    @ManyToOne(fetch = FetchType.LAZY)
    private User user;

    private Timestamp lastUpdated;

    public MlpConfig(String name, String description, int batchSize, int epochs, Set<Layer> layers,
            ActivationFunction activationFunction, User user) {
        this.name = name;
        this.description = description;
        this.batchSize = batchSize;
        this.epochNumber = epochs;
        this.activationFunction = activationFunction;
        this.layers = layers;
        this.lastUpdated = Timestamp.from(Instant.now());
        this.user = user;
    }

方法的调用:

@Transactional
@GetMapping("/getAllConfigs")
public ResponseEntity<Object> getAllMlpConfig(@RequestHeader HttpHeaders headers, Authentication authentication) {
    User user = userService.findByUsername(authentication.getName());
    List<MlpConfig> configs = mlpConfigService.findAllByUser_id(user.getId());

    return ResponseEntity.status(HttpStatus.OK).body(configs);
}

实体ActivationFunction:

@Entity
@Data
@NoArgsConstructor
@Table(name = "activationFunctions")
public class ActivationFunction {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Enumerated(EnumType.STRING)
    @Column(length = 20)
    private EActivationFunction type;

    @ToString.Exclude
    @OneToMany(mappedBy = "activationFunction")
    private Set<MlpConfig> mlpConfig;

    public ActivationFunction(EActivationFunction type) {
        this.type = type;
    }
}

那么该如何处理呢？我刚刚发现 Spring MVC 的这个解决方案看起来很旧。

Answer 1

我实际上可以在一整天后解决这个问题。

根据此答案的评论 https://stackoverflow.com/a/37840526/10565504 :

对于 Gradle，我将此行添加到我的 build.gradle

compile group: 'com.fasterxml.jackson.datatype', name: 'jackson-datatype-hibernate5', version: '2.11.0'

为了让它工作，我添加了:

@Bean
public Module datatypeHibernateModule() {
    return new Hibernate5Module();
}

后来我不得不承认我的代码中有无限递归。我可以用以下答案修复它:https://stackoverflow.com/a/18288939/10565504

另一个问题是我在 MlpConfig 实体中的字段 activationFunction 上使用了 @ToString.Exclude 注释。没有 toString 的传入值始终为 null。

//@EqualsAndHashCode.Exclude
//@ToString.Exclude
@ManyToOne(fetch = FetchType.LAZY)
private ActivationFunction activationFunction;