Cộng đồng Hỏi & Đáp của Inflearn

class Item(
    id: Long,
    orderId: String,
) {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Long = id

    var orderId: String = orderId


    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "shipping_id")
    var shipping: Shipping? = null

}

@Entity
class Shipping(
) {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Long = id

    @Embedded
    var trackingInformation: TrackingInformation? = null


    @OneToMany(mappedBy = "shipping", cascade = [CascadeType.ALL], fetch = FetchType.LAZY)
    var items: MutableList<Item> = mutableListOf()


    fun updateTrackingInformation(trackingInformation: TrackingInformation) {
        this.trackingInformation = trackingInformation
    }

}

// 위처럼 양방향 연관관계를 맺었는데
// 이것도 되고

class Facade(
    private val shippingService: ShippingService,
    private val itemService: ItemService,
) {

    fun getResult(pipeline: String) {
       
       val shipping = shippingService.getShippings(listOf("0000000003")).first()
        shipping.items.first().setOrderId("test")

        shippingService.save(shipping)
    }
}

// 이것도 됩니다.

class Facade(
    private val shippingService: ShippingService,
    private val itemService: ItemService,
) {

    fun getResult(pipeline: String) {
            val item = itemService.getItemByKitSlug(result.kitSlug)
            item.shipping.updateTrackingInformation(trackingInformation)

            itemService.save(item)

    }
}

mappedBy로 된 shipping.items 필드로 접근하면 insert, update가 안될 거라고 생각했는데 
둘다 변경이 되어서 질문드립니다.

제가 어떤 점을 놓치고 있는 걸까요?