Kotlin继承：在序列化和反序列化到/从json之后对象不相等

Question

我有继承的 kotlin 类：

abstract class Classification(
        val accuracy: Double
)

@Document
class OrderForm(
        @Id
        val id: String,
        accuracy: Double,
        val customerNumber: String,
        val orders: List<Order>
) : Classification(accuracy)

并且我实现了一个序列化测试：

internal class OrderFormTest : Logging {

    private val objectMapper = ObjectMapper().registerKotlinModule()

    @Test
    fun canBeSerialisedToJsonAndBack() {
        val expected = OrderForm(
                "123_ID",
                94.77,
                "123_CUSTOMER",
                listOf(
                        Order(
                                0.0,
                                OrderNumber(
                                        10.0,
                                        123456789L),
                                OrderSize(
                                        99.99,
                                        "38/40"),
                                OrderAmount(
                                        100.0,
                                        7),
                                OrderPrice(
                                        50.0,
                                        999.99),
                                OrderPage(
                                        23.29343,
                                        100)
                        ),
                        Order(
                                0.0,
                                OrderNumber(
                                        10.0,
                                        123456789L),
                                OrderSize(
                                        99.99,
                                        "38/40"),
                                OrderAmount(
                                        100.0,
                                        7),
                                OrderPrice(
                                        50.0,
                                        999.99),
                                OrderPage(
                                        23.29343,
                                        100)
                        )
                )
        )

        logger.info("expected: $expected")

        val json = objectMapper.writeValueAsString(expected)

        logger.info("json: $json")

        val result: OrderForm = objectMapper.readValue(json)

        logger.info("result: $result")

        val json2 = objectMapper.writeValueAsString(result);

        logger.info("json: $json2")

        Assertions.assertThat(result).isEqualTo(expected)
    }
}

日志输出：

14:57:37.031 [main] OrderFormTest - expected: de.fronetic.witt.ml.backend.model.OrderForm@4b34fff9
14:57:37.623 [main] OrderFormTest - json: {"id":"123_ID","accuracy":94.77,"customerNumber":"123_CUSTOMER","orders":[{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}},{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}}]}
14:57:37.673 [main] OrderFormTest - result: de.fronetic.witt.ml.backend.model.OrderForm@38b972d7
14:57:37.674 [main] OrderFormTest - json: {"id":"123_ID","accuracy":94.77,"customerNumber":"123_CUSTOMER","orders":[{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}},{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}}]}

所以对象的内容完全一样，但对象本身不相等！

如果我不使用继承，这不会发生：

@Document
data class OrderForm(
        @Id
        val id: String,
        val accuracy: Double,
        val customerNumber: String,
        val orders: List<Order>
)

日志输出：

14:59:03.889 [main] OrderFormTest - expected: OrderForm(id=123_ID, accuracy=94.77, customerNumber=123_CUSTOMER, orders=[Order(accuracy=0.0, orderNumber=OrderNumber(accuracy=10.0, number=123456789), orderSize=OrderSize(accuracy=99.99, size=38/40), orderAmount=OrderAmount(accuracy=100.0, amount=7), orderPrice=OrderPrice(accuracy=50.0, price=999.99), orderPage=OrderPage(accuracy=23.29343, page=100)), Order(accuracy=0.0, orderNumber=OrderNumber(accuracy=10.0, number=123456789), orderSize=OrderSize(accuracy=99.99, size=38/40), orderAmount=OrderAmount(accuracy=100.0, amount=7), orderPrice=OrderPrice(accuracy=50.0, price=999.99), orderPage=OrderPage(accuracy=23.29343, page=100))])
14:59:04.833 [main] OrderFormTest - json: {"id":"123_ID","accuracy":94.77,"customerNumber":"123_CUSTOMER","orders":[{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}},{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}}]}
14:59:04.913 [main] OrderFormTest - result: OrderForm(id=123_ID, accuracy=94.77, customerNumber=123_CUSTOMER, orders=[Order(accuracy=0.0, orderNumber=OrderNumber(accuracy=10.0, number=123456789), orderSize=OrderSize(accuracy=99.99, size=38/40), orderAmount=OrderAmount(accuracy=100.0, amount=7), orderPrice=OrderPrice(accuracy=50.0, price=999.99), orderPage=OrderPage(accuracy=23.29343, page=100)), Order(accuracy=0.0, orderNumber=OrderNumber(accuracy=10.0, number=123456789), orderSize=OrderSize(accuracy=99.99, size=38/40), orderAmount=OrderAmount(accuracy=100.0, amount=7), orderPrice=OrderPrice(accuracy=50.0, price=999.99), orderPage=OrderPage(accuracy=23.29343, page=100))])
14:59:04.914 [main] OrderFormTest - json: {"id":"123_ID","accuracy":94.77,"customerNumber":"123_CUSTOMER","orders":[{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}},{"accuracy":0.0,"orderNumber":{"accuracy":10.0,"number":123456789},"orderSize":{"accuracy":99.99,"size":"38/40"},"orderAmount":{"accuracy":100.0,"amount":7},"orderPrice":{"accuracy":50.0,"price":999.99},"orderPage":{"accuracy":23.29343,"page":100}}]}

为什么会这样？

Answer 1

问题不在于继承 VS 没有继承本身。

在一种情况下，您使用的是data class（它会自动生成equals() 方法），而在另一种情况下，您使用的是标准的class，它没有任何魔力。

在标准类中，你需要自己实现equals()（或者在你的IDE的帮助下生成它）。