如何根据 Kotlin 中的唯一键值检索 Firebase 数据

Question

我在这里从Firebase数据库中获取所有"items"条目。 实际上需要它只给我特定unique key条目

ref = FirebaseDatabase.getInstance().getReference().child("Sales")
ref.addValueEventListener(object : ValueEventListener{
override fun onCancelled(p0: DatabaseError) {
}
override fun onDataChange(p0: DataSnapshot) {
ref.addListenerForSingleValueEvent(object : ValueEventListener {
override fun onCancelled(p0: DatabaseError) {
}
override fun onDataChange(p1: DataSnapshot) {
println("onDataChange")
if (p0.exists()) {
list.clear()
for (h in p0.children) {
if (h.hasChild("items")) {
val generic: GenericTypeIndicator<ArrayList<Product>> =  object : GenericTypeIndicator<ArrayList<Product>>() {}
val items = h.child("items").getValue(generic)
items?.let { productList.addAll(it) }
}
val adapter = ReceiptItemsAdapter(applicationContext, productList)
rReceyclerView.adapter = adapter
}
}
}
})
}
})

我已经尝试过这样，但它没有用，也没有给出任何错误。

ref = FirebaseDatabase.getInstance().getReference().child("Sales/-Lw37uyfuBA0AfTalp")

这是我的 JSON 文件

{
"-Lw37uyfuBA0AfTalp": {
"date": "14/12/2019",
"discount": 0.24,
"due": 0,
"items": [
{
"pamount": 2.4,
"pname": "Granola",
"pprice": 2.4,
"punit": 1
}
],
"paym": [
{
"paymentAmnt": 0.02,
"paymentDesc": "Cash Payment :"
},
{
"paymentAmnt": 2.14,
"paymentDesc": "Card Payment :"
}
],
"subTotal": 2.4,
"time": "11:16:42",
"total": 2.16
},
"-Lw5Qx8sVdw3ZCMiXAL-": {
"date": "14/12/2019",
"discount": 1,
"due": 0,
"items": [
{
"pamount": 4.8,
"pname": "Granola",
"pprice": 2.4,
"punit": 2
},
{
"pamount": 2.6,
"pname": "Brownie",
"pprice": 2.6,
"punit": 1
},
{
"pamount": 2.6,
"pname": "Brownie",
"pprice": 2.6,
"punit": 1
}
],
"name": "James Brown",
"paym": [
{
"paymentAmnt": 3,
"paymentDesc": "Cash Payment :"
},
{
"paymentAmnt": 5,
"paymentDesc": "Staff Markout :"
},
{
"paymentAmnt": 1,
"paymentDesc": "Card Payment :"
}
],
"subTotal": 10,
"time": "22:03:07",
"total": 9
},
"-Lw5T4TfYUTXsWKAndBx": {
"date": "14/12/2019",
"discount": 0.24,
"due": -0.84,
"items": [
{
"pamount": 2.4,
"pname": "Granola",
"pprice": 2.4,
"punit": 1
}
],
"name": "James Brown",
"paym": [
{
"paymentAmnt": 3,
"paymentDesc": "Cash Payment :"
}
],
"subTotal": 2.4,
"time": "22:12:26",
"total": 2.16
},
"-Lw5UWguHS18IwWE6elT": {
"date": "14/12/2019",
"discount": 0.26,
"due": -1.66,
"items": [
{
"pamount": 2.6,
"pname": "Brownie",
"pprice": 2.6,
"punit": 1
}
],
"name": "James Brown",
"paym": [
{
"paymentAmnt": 4,
"paymentDesc": "Cash Payment :"
}
],
"subTotal": 2.6,
"time": "22:18:43",
"total": 2.34
},
"-Lw5ypp5xJLJO53bjejk": {
"date": "15/12/2019",
"discount": 0,
"due": -1.6,
"items": [
{
"pamount": 2.4,
"pname": "Granola",
"pprice": 2.4,
"punit": 1
}
],
"name": "James Brown",
"paym": [
{
"paymentAmnt": 4,
"paymentDesc": "Cash Payment :"
}
],
"subTotal": 2.4,
"time": "00:35:32",
"total": 2.4
},
"-LwANPC0UYCmTnqm7DRV": {
"date": "15/12/2019",
"discount": 1,
"due": 0,
"items": [
{
"pamount": 2.4,
"pname": "Granola",
"pprice": 2.4,
"punit": 1
},
{
"pamount": 2.6,
"pname": "Brownie",
"pprice": 2.6,
"punit": 1
},
{
"pamount": 2.4,
"pname": "Granola",
"pprice": 2.4,
"punit": 1
},
{
"pamount": 2.6,
"pname": "Brownie",
"pprice": 2.6,
"punit": 1
}
],
"name": "James Brown",
"paym": [
{
"paymentAmnt": 5,
"paymentDesc": "Cash Payment :"
},
{
"paymentAmnt": 4,
"paymentDesc": "Card Payment :"
}
],
"subTotal": 10,
"time": "21:05:43",
"total": 9
}
}

谁能告诉我，我哪里做错了？

谢谢。

编辑零件 .... 产品类别

data class Product(var pName: String = "", var pUnit: Int = 1, var pPrice: Double = 00.00, var pAmount: Double = 00.00) : Parcelable {
constructor(parcel: Parcel) : this(
parcel.readString(),
parcel.readInt(),
parcel.readDouble(),
parcel.readDouble()
)
override fun writeToParcel(parcel: Parcel, flags: Int) {
parcel.writeString(pName)
parcel.writeInt(pUnit)
parcel.writeDouble(pPrice)
parcel.writeDouble(pAmount)
}
override fun describeContents(): Int {
return 0
}
companion object CREATOR : Parcelable.Creator<Product> {
override fun createFromParcel(parcel: Parcel): Product {
return Product(parcel)
}
override fun newArray(size: Int): Array<Product?> {
return arrayOfNulls(size)
}
}

另外，该部分在这里尝试。

val rootRef = FirebaseDatabase.getInstance().reference
val ref = rootRef.child("Sales").child("-LwIWKf-CTNTdwi4iMLU")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val product = dataSnapshot.getValue(Product::class.java)
//println("pname : "+product?.pName)
Log.d(TAG, product!!.pName)
}
override fun onCancelled(databaseError: DatabaseError) {
// Log.d("TAG", databaseError.getMessage()) //Don't ignore errors!
}
}
ref.addListenerForSingleValueEvent(valueEventListener)

另外，尝试了彼得的解决方案，它有效，但我需要将"项目"作为数组列表 谢谢

Answer 1

您应该执行以下操作：

ref = FirebaseDatabase.getInstance().getReference().child("Sales").child("-Lw37uyfuBA0AfTalp")
ref.addValueEventListener(object : ValueEventListener{
override fun onCancelled(p0: DatabaseError) {
}
override fun onDataChange(p0: DataSnapshot) {
println("onDataChange")
if (p0.exists()) {
val date = p0.child("date").getValue(String::class.java)
val discount = p0.child("discount").getValue(String::class.java)
}
}
})

这将为您提供唯一键下的数据

Answer 2

实际上需要它只给我来自特定唯一键的条目

要从特定的唯一键(例如-Lw37uyfuBA0AfTalp(获取条目，请使用以下代码行：

val rootRef = FirebaseDatabase.getInstance().reference
val ref = rootRef.child("Sales").child("-Lw37uyfuBA0AfTalp")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val product = dataSnapshot.getValue(Product::class.java)
Log.d(TAG, product!!.time)
}
override fun onCancelled(databaseError: DatabaseError) {
Log.d(TAG, databaseError.getMessage()) //Don't ignore errors!
}
}
ref.addListenerForSingleValueEvent(valueEventListener)

日志中的输出将是：

11:16:42

我刚刚添加了一个日志语句以查看它是否有效。

编辑：

根据您的评论，如果您想获得产品列表，请使用以下代码行：

val rootRef = FirebaseDatabase.getInstance().reference
val salesRef = rootRef.child("Sales")
val valueEventListener = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
val productList = arrayListOf<Product>()
for (ds in dataSnapshot.children) {
val product = ds.getValue(Product::class.java)
productList.add(product)
Log.d(TAG, product!!.time)
}
//Do what you need to do with your list
}
override fun onCancelled(databaseError: DatabaseError) {
Log.d(TAG, databaseError.getMessage()) //Don't ignore errors!
}
}
salesRef.addListenerForSingleValueEvent(valueEventListener)