jackson ObjectMapperHibernate问题

Question

我正在开发一个spring boot 2.0/Java 8购物车在线应用程序。我使用Hibernate作为ORM框架。我有两个实体，Order和OrderDetail，如下所示：

@Entity
@Table(name = "orders")
public class Order extends AbstractEntityUuid {

    @Column(name = "order_number", unique = true)
    private String orderNumber;

    @JsonBackReference
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User user;

    @Column(name = "total_amount")
    private BigDecimal totalAmount = BigDecimal.ZERO;

    @CreatedDate
    @Column(name = "created_on", columnDefinition = "DATETIME", updatable = false)
    protected LocalDateTime created;

    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    @JsonManagedReference
    private Set<OrderDetail> items = new HashSet<>();

    @OneToOne(fetch = FetchType.LAZY, orphanRemoval = true)
    @JoinColumn(nullable = false, name = "card_details_id")
    private CardDetails card;

    @OneToOne(fetch = FetchType.LAZY, orphanRemoval = true)
    @JoinColumn(nullable = false, name = "shipping_address_id")
    private Address shippingAddress;

    @OneToOne(fetch = FetchType.LAZY, orphanRemoval = true)
    @JoinColumn(name = "billing_address_id")
    private Address billingAddress;

    //getters and setters
}

@Entity
@Table(name = "order_detail")
public class OrderDetail extends AbstractPersistable<Long> {

    @Column(name = "quantity")
    private Integer quantity;

    @Column(name = "total_amount")
    private BigDecimal totalAmount = BigDecimal.ZERO;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "order_id", nullable = false)
    @JsonBackReference
    private Order order;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "product_id", nullable = false)
    private Product product;

    //getters and setters
}

当用户转向他的订单时，他应该能够看到仅与订单本身相关的信息（没有详细信息）。因此，我只从order表中检索数据。以下是我的存储库：

public interface OrderRepository extends CrudRepository<Order, Long> {

    @Query("FROM Order o WHERE o.user.email = ?1")
    List<Order> findOrdersByUser(String email);
}

在服务中，我所做的只是调用上面的方法并将其转换为dto对应方。

@Transactional(readOnly = true)
public List<OrdersPreviewDTO> getOrdersPreview(String email) {
    List<Order> orders = orderRepository.findOrdersByUser(email);
    return orderConverter.convertToOrderPreviewDTOs(orders);
}

转换器在引擎盖下使用了一个jackson的objectmapper对象。

List<OrdersPreviewDTO> convertToOrderPreviewDTOs(List<Order> orders) {
    return orders.stream()
     .map(o -> objectMapper.convertValue(o, OrdersPreviewDTO.class))
     .collect(toList());
}

ObjectMapper由spring注入，并在配置类中定义：

@Bean
public ObjectMapper objectMapper() {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.findAndRegisterModules();
    return objectMapper;
}

OrderspReviewDTOdto对象只包含Order实体的一个子集，因为正如我已经提到的，在Orders页面中，我只想显示用户订单的高级属性，而不是与其详细信息相关的属性。

@JsonIgnoreProperties(ignoreUnknown = true)
public class OrdersPreviewDTO {

    private String orderNumber;

    @JsonFormat(pattern = "dd/MM/yyyy HH:mm")
    private LocalDateTime created;

    private BigDecimal totalAmount;

    @JsonCreator
    public OrdersPreviewDTO(
            @JsonProperty("orderNumber") String orderNumber,
            @JsonProperty("created") LocalDateTime created,
            @JsonProperty("totalAmount") BigDecimal totalAmount) {
        this.orderNumber = orderNumber;
        this.created = created;
        this.totalAmount = totalAmount;
    }

    //getters and setters
}

一切工作正常，订单实体自动转换为它的dto对应的jackson。当查看Hibernate在引擎盖下执行的查询时，问题就出来了。Hibernate打开每个订单的订单详细信息集合，并执行一个查询以从每个子集合检索数据：

select carddetail0_.id as id1_2_0_, carddetail0_.brand as brand2_2_0_, carddetail0_.created as created3_2_0_, carddetail0_.exp_month as exp_mont4_2_0_, carddetail0_.exp_year as exp_year5_2_0_, carddetail0_.last4 as last6_2_0_ from card_details carddetail0_ where carddetail0_.id=?

select address0_.id as id1_1_0_, address0_.created as created2_1_0_, address0_.last_modified as last_mod3_1_0_, address0_.city as city4_1_0_, address0_.country as country5_1_0_, address0_.first_name as first_na6_1_0_, address0_.last_name as last_nam7_1_0_, address0_.postal_code as postal_c8_1_0_, address0_.state as state9_1_0_, address0_.street_address as street_10_1_0_, address0_.telephone as telepho11_1_0_ from address address0_ where address0_.id=?

select items0_.order_id as order_id4_4_0_, items0_.id as id1_4_0_, items0_.id as id1_4_1_, items0_.order_id as order_id4_4_1_, items0_.product_id as product_5_4_1_, items0_.quantity as quantity2_4_1_, items0_.total_amount as total_am3_4_1_ from order_detail items0_ where items0_.order_id=?

还有更多的人。

无论我以以下方式修改代码，Hibernate都只在Order表上运行预期的查询：

这行代码：

objectMapper.convertValue(o, OrdersPreviewDTO.class)

被以下脏修复替换：

new OrdersPreviewDTO(o.getOrderNumber(), o.getCreated(), o.getTotalAmount())

由Hibernate运行的查询：

select order0_.id as id1_5_, order0_.billing_address_id as billing_6_5_, order0_.card_details_id as card_det7_5_, order0_.created_on as created_2_5_, order0_.one_address as one_addr3_5_, order0_.order_number as order_nu4_5_, order0_.shipping_address_id as shipping8_5_, order0_.total_amount as total_am5_5_, order0_.user_id as user_id9_5_
from orders order0_ cross join user user1_
where order0_.user_id=user1_.id and user1_.user_email=?

我的问题是。有没有一种方法告诉jackson只映射Dtos字段，这样它就不会通过Hibernate触发非必需字段的惰性加载提取？

谢谢

Answer 1

埃塞克斯郡男孩回答+1。我只想补充一点，您可以直接从您的JPQL查询返回DTO而不是使用jackson。它避免了从数据库到对象order的转换，然后又从order对象到orderspreviewdto对象的转换。

例如，您需要更改存储库中的查询来完成此操作。这可能是这样的：

public interface OrderRepository extends CrudRepository<Order, Long> {

    @Query("SELECT new OrdersPreviewDTO(o.order_number, o.created_on, o.total_amount)) FROM Order o WHERE o.user.email = ?1")
    List<OrdersPreviewDTO> findOrdersByUser(String email);
}

Answer 2

简短的答案是否定的，不要尝试和这么聪明，手动创建您的DTO来控制任何懒散加载，然后在事务外部的DTO上使用jackson。

很长的答案是肯定的，您可以覆盖MappingJackson2HttpMessageConverter并控制从实体调用哪些字段。

@Configuration
public class MixInWebConfig extends WebMvcConfigurationSupport {

    @Bean
    public MappingJackson2HttpMessageConverter customJackson2HttpMessageConverter2() {
        MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.addMixIn(DTO1.class, FooMixIn.class);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        jsonConverter.setObjectMapper(objectMapper);
        return jsonConverter;
    }

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(customJackson2HttpMessageConverter2());
    }
}

然后

    @Override
    protected void processViews(SerializationConfig config, BeanSerializerBuilder builder) {
        super.processViews(config, builder);
        if (classes.contains(builder.getBeanDescription().getBeanClass())) {
            List<BeanPropertyWriter> originalWriters = builder.getProperties();
            List<BeanPropertyWriter> writers = new ArrayList<BeanPropertyWriter>();
            for (BeanPropertyWriter writer : originalWriters) {
                String propName = writer.getName();
                if (!fieldsToIgnore.contains(propName)) {
                    writers.add(writer);
                }
            }
            builder.setProperties(writers);
        }
    }
}

这里有一个工作示例。