Can't save same Kotlin data class multiple times with ToMany

Issue Basics

• ObjectBox version (are using the latest version?): 2.0.0
• Reproducibility: always

Reproducing the bug

Description

I'm using ObjectBox to save data. When I save the same data with ToMany, it only save the first one.

I write a test, the size of result.details is 1.

Can I save multiple same data with ToMany? How can I fix it?

Thanks for answer.

ObjectBox(version:2.0.0)
Android(target sdk version:27)
Kotlin(version:1.2.60)

Code

@Test
fun orderDetailTest() {
    val orderBox: Box<Order> = store.boxFor()

    // 儲存兩個內容相同的資料
    val order = Order().apply {
        this.details.add(OrderDetail(productSpecName = "ABC"))
        this.details.add(OrderDetail(productSpecName = "ABC"))
    }

    val orderId = orderBox.put(order)

    val result = orderBox.get(orderId)

    assert(result.details.size == 2)
}

Entities

@Entity
data class Order(@Id var id: Long = 0,
                 val createTime: Long = 0,
                 val total: Int = 0) {

    @Backlink(to = "order")
    lateinit var details: ToMany<OrderDetail>
}

@Entity
data class OrderDetail(@Id var id: Long = 0,
                       val productName: String = "",
                       val productSpecName: String = "",
                       val productSpecPrice: Int = 0,
                       val quantity: Int = 0,
                       val subtotal: Int = 0) {

    lateinit var order: ToOne<Order>
}

Inizia riproducendo il caso orderDetailTest con le entità Order e OrderDetail mostrate, quindi esamina come vengono persistiti il backlink ToMany e la relazione ToOne. Il lavoro è completato quando il salvataggio di due istanze OrderDetail identiche restituisce result.details.size == 2, oppure quando viene documentata la limitazione prevista.