Question

我将Spring JPA与hibernate，WebFlux结合使用时遇到了问题。我试图从数据库中获取某些实体，但是当我尝试将实体转换为DTO时发生了延迟加载异常。我理解为什么会发生这种情况，我可以通过创建DTO的每个实体图（仅获取渴望的属性）来避免发生这种情况，但这似乎是过大了。我也尝试使用setPropertyCondition()和Hibernate.isInitialized()跳过惰性属性，但是在模型映射器检查属性条件之前引发了异常。我试图在映射中返回实体对象，但找不到杰克逊Hibernate5Module用法的正确配置。因此，我问你如何在仓库中使用@EntityGraph来确保控制器没有错误，理想情况下，延迟加载的属性应该为null。

我通过在DTO映射过程中跳过延迟属性来解决延迟初始化异常的问题。我为此创建了自己的值读取器，并将其应用于Java模型映射器实例。

public class CustomValueReader implements ValueReader<Object> {
    @Override
    public Object get(Object source, String memberName) {
        try {
            Field field = source.getClass().getDeclaredField(memberName);
            field.setAccessible(true);
            return field.get(source);
        }
        catch(Exception e) {
            return null;
        }
    }

    @Override
    public Member<Object> getMember(Object source, String memberName) {
        final Object value = get(source, memberName);
        Class<?> memberType = value != null ? value.getClass() : Object.class;
        return new Member<Object>(memberType) {
            @Override
            public Object getOrigin() {
                return null;
            }

            @Override
            public Object get(Object source, String memberName) {
                return CustomValueReader.this.get(source, memberName);
            }
        };
    }

    @Override
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public Collection<String> memberNames(Object source) {
        List<String> properties = new ArrayList<>();
        for (Field field : source.getClass().getDeclaredFields()) {
            field.setAccessible(true);//needed for accessing field using reflection
            boolean valid = true;
            Object fieldValue = null;
             try{
                 fieldValue = field.get(source);
             }
             catch(Exception e) {
                 valid = false;
             }
            boolean isInited = valid && Hibernate.isInitialized(fieldValue);
             if (isInited){
                 properties.add(field.getName());
             }
        }
        return properties;
    }

    @Override
    public String toString() {
        return "Costum";
    }
}

将其应用于映射器

mapper.getConfiguration().addValueReader(new CustomValueReader());

我还注意到实体图的使用使所有属性渴望或懒散（取决于EntityGraph.EntityGraphType）而忽略attributeNodes。我的班级定义看起来像

@NamedEntityGraphs({
        @NamedEntityGraph(name = ClinicVisit.CLINIC_VISIT_ENTITY_GRAPH_WITH_PATIENT_AND_DEVICES,
                attributeNodes = @NamedAttributeNode(value = "patient",subgraph = "CVEG_DEVICES"),
                subgraphs = @NamedSubgraph(name = "CVEG_DEVICES", attributeNodes = @NamedAttributeNode("notificationDevices"))
        ),
        @NamedEntityGraph(name = ClinicVisit.CLINIC_VISIT_ENTITY_GRAPH_WITH_PATIENT,
                attributeNodes = @NamedAttributeNode(value = "patient")
        )
})


@Entity
@Table(name="clinic_visit_request")
@Getter
@Setter
public class ClinicVisit {

    public final static String CLINIC_VISIT_ENTITY_GRAPH_WITH_PATIENT_AND_DEVICES = "clinic_visit_request_patient_devices";
    public final static String CLINIC_VISIT_ENTITY_GRAPH_WITH_PATIENT = "clinic_visit_request_patient";

    @Id
    @GeneratedValue
    protected Long id;

    @Column(name = "visit_date")
    protected Date visitDate;

    @Column(name = "update_date")
    protected Date updateDate;

    protected Boolean informed;

    @Column( columnDefinition = "boolean default false", nullable = false)
    protected Boolean handled = false;

    @ManyToOne()
    protected ClinicUser doctor;

    @ManyToOne()
    protected ClinicUser patient;

    @ManyToOne()
    protected ClinicUser confirmer;
}

我的存储库方法定义：

@EntityGraph(value=ClinicVisit.CLINIC_VISIT_ENTITY_GRAPH_WITH_PATIENT,type= EntityGraph.EntityGraphType.FETCH)
   List<ClinicVisit> findAll();

一切正常，这是我的误解。我有三个字段（医生，患者，确认者），并在其中保存了相同的用户，因此，当我为患者添加NamedAttributeNode时，我希望只加载患者，但由于休眠很聪明，所以会加载其他字段。

我了解为什么Hibernate5Module无法正常工作。我使用WebFlux，因此JacksonMapper的配置应如下所示：

@Configuration
public class AppConfig {

@Bean
Jackson2ObjectMapperBuilderCustomizer jackson2ObjectMapperBuilderCustomizer(){
    return jacksonObjectMapperBuilder -> jacksonObjectMapperBuilder
            .featuresToEnable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
            .propertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE)
            .modules(new Hibernate5Module());
}


@Bean
Jackson2JsonEncoder jackson2JsonEncoder(ObjectMapper mapper){
    return new Jackson2JsonEncoder(mapper);
}

@Bean
Jackson2JsonDecoder jackson2JsonDecoder(ObjectMapper mapper){
    return new Jackson2JsonDecoder(mapper);
}

@Bean
WebFluxConfigurer webFluxConfigurer(Jackson2JsonEncoder encoder, Jackson2JsonDecoder decoder) {
    return new WebFluxConfigurer() {
        @Override
        public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
            configurer.defaultCodecs().jackson2JsonEncoder(encoder);
            configurer.defaultCodecs().jackson2JsonDecoder(decoder);
        }
    };
}

}

Answer 1

设置Hibernate5Module就像创建bean一样容易：

@Bean
public com.fasterxml.jackson.databind.Module datatypeHibernateModule() {
    return new Hibernate5Module();
}

请参见https://stackoverflow.com/a/37840526/10609423

与Spring Boot 2.1.2完美配合。如果可以的话，我会发表评论。

如何使用Java模型映射器将具有惰性属性的实体转换为DTO

1 个答案: