使用kotlin从firebase实时检索/获取嵌套节点对象

Question

我想从嵌套节点中的日期获取数据对象(地址，check_in, check_out)。

我的数据库是这样的:

---`attendance` :{
|
|---danielle:{ <---------- here is username, node of `attendance`
|   |
|   |---2023-04-08: <----------- here is the date she checked in and out for work
|   |   |
|   |   |---address: "Thomas street"
|   |   |
|   |   |---check_in: "09:02 AM"
|   |   |
|   |   |---check_out: "06:30 PM"
|   |
|   |
|    ---2023-04-10":
|       |
|       |---address: "Maria street"
|       |
|       |---check_in: "09:02 AM"
|       |
|        ---check_out: "06:30 PM"
|
---mark:{ <---------- here is another username
|
|---2023-04-07: <----------- here is the date he checked in and out for work
|   |
|   |---address: "Thomas street"
|   |
|   |---check_in: "09:02 AM"
|   |
|   |---check_out: "06:30 PM"
|
|
---2023-04-11":
|
|---address: "Maria street"
|
|---check_in: "10:23 AM"
|
---check_out: "08:30 PM"          

我尝试使用这个编码

val attModel = arrayListOf<AttendanceModel>()
Firebase.database.getReference("Attendance").child("danielle").child("2023-04-08").addValueEventListener(object : ValueEventListener {
override fun onDataChange(snapshot: DataSnapshot) {
for (h in snapshot.children) {
val data = h.getValue(AttendanceModel::class.java)
attModel.add(data!!)
}
}
}

但是我得到了这个错误

Android : com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to AttendanceModel

我知道danielle确实是一个String，但我不明白它是如何得到一个错误的，因为danielle有一个对象节点在里面。

我也尝试了这个编码在这里，我试图嵌套路径2023-04-08

val todays = arrayListOf<AttendanceModel>()
Firebase.database.getReference("Attendance").child("danielle")
.addValueEventListener(object : ValueEventListener {
override fun onDataChange(snapshot: DataSnapshot) {
for (h in snapshot.children) {
val date = h.child("2023-04-08")
for (i in date.children) {
val dataUser = i.getValue(AttendanceModel::class.java)
todays.add(dataUser!!)
}

在模拟器不返回任何东西，然后我试图记录dataUser，它给了我

DataSnapshot { key = danielle, value = null }

这是我的数据类

data class AttendanceModel(
val loc_name: String? = "",
val address: String? = "",
val check_in: String? = "",
val check_out: String? = ""
)

任何形式的帮助将是如此感激!

Answer 1

当您在2023-04-08上附加侦听器时，不需要迭代，您可以直接读取子节点的值，或者您可以将节点映射到AttendanceModel类型的对象。在代码中，它就像这样简单:

val db = Firebase.database.reference
val dateRef = db.child("attendance/danielle/2023-04-08")
dateRef.get().addOnCompleteListener {
if (it.isSuccessful) {
val snapshot = it.result
val key = snapshot.key
Log.d(TAG, "key: $key")
val data = snapshot.getValue(AttendanceModel::class.java)
Log.d(TAG, "data: ${data.address}${data.check_in}/${data.check_out}")
} else {
Log.d(TAG, "${it.exception?.message}") //Never ignore potential errors!
}
}

日志的结果将是:

key: 2023-04-08
data: Thomas street/09:02 AM/06:30 PM

Answer 2

不需要迭代快照子，因为已经获取了整个对象的日期。如果使用迭代，它将为对象内的每个键返回值。

代替

for (h in snapshot.children) {
val data = h.getValue(AttendanceModel::class.java)
attModel.add(data!!)
}

val data = snapshot.getValue(AttendanceModel::class.java)
attModel.add(data!!)