Firestore update array field in a Document - firebase

Question

I have a document like below, in my document, have a Array . in array have Objects. How can i update new object to an Array.
As you see below i can add document in a colletion wit an array, but when i tried to update it gives error
java.lang.IllegalArgumentException: Invalid data. Unsupported type: com.test.data.modal.Product
What i tried;
var pid = ""
btnAdd.setOnClickListener {
val list = ArrayList<Product>()
list.add(Product("u1", "1", 1))
list.add(Product("u2", "2", 1))
list.add(Product("u3", "3", 1))
val testObject = TestObject("Talha", "Kosen", list)
FirebaseFirestore.getInstance().collection("Test")
.add(testObject)
.addOnCompleteListener { task ->
pid = task.result.id
}
}
btnUpdate.setOnClickListener {
val list = ArrayList<Product>()
list.add(Product("u1", "1", 1))
list.add(Product("u2", "2", 1))
list.add(Product("u3", "3", 1))
list.add(Product("u4", "4", 4))
FirebaseFirestore.getInstance()
.collection("Test")
.document(pid)
.update("product", list)
}
document:
POJO:
#IgnoreExtraProperties
#Keep
class TestObject {
var name: String = ""
var surname: String = ""
lateinit var productList: List<Product>
constructor()
constructor(name: String, surname: String, productList: List<Product>) {
this.name = name
this.surname = surname
this.productList = productList
}
}
#IgnoreExtraProperties
#Keep
class Product {
var imagePath: String = ""
var productUrl: String = ""
var brand: Int = 0
constructor()
constructor(imagePath: String, productUrl: String, brand: Int) {
this.imagePath = imagePath
this.productUrl = productUrl
this.brand = brand
}
}

Answer 1

I have probably not the answer but this could help :
You try to update with an ArrayList but you store a List (in your TestObject)
Refer to the documentation to update fields in nested objects https://firebase.google.com/docs/firestore/manage-data/add-data#update_fields_in_nested_objects
It could be a good idea to store a collection in your TestObject document instead of a list ? You'll able to update easily your fields