从 firebase 获取最后 child

Question

我正在尝试向我的 firebase 添加游乐设施，我正在使用以下代码：

dbref = FirebaseDatabase.getInstance().getReference("Users")
        databaseQuery = myRef.orderByKey().limitToLast(1)
        firebaseAuth = FirebaseAuth.getInstance()


      databaseQuery.addValueEventListener(object : ValueEventListener {
            override fun onDataChange(snapshot: DataSnapshot) {
              var BuleiaId = 0
                for (snapshot in snapshot.children){
                    var viagem = snapshot.getValue(Buleia::class.java)
                    BuleiaId = viagem?.id!!
                }
            }

            override fun onCancelled(error: DatabaseError) {
                TODO("Not yet implemented")
            }
        })

        dbref.addValueEventListener(object : ValueEventListener {

            override fun onDataChange(snapshot: DataSnapshot) {
                if (snapshot.exists()) {

                    for (userSnapshot in snapshot.children) {
                        val user = userSnapshot.getValue(User::class.java)
                        if (user?.userId == firebaseAuth.currentUser?.uid) {
                            var user = user?.userName
                            button = findViewById(R.id.ButtonAdicionaBoleia)
                            button.setOnClickListener {
                                

                                var id = BuleiaId+1
                                var rideDay = findViewById<EditText>(R.id.rideDay).text
                                var rideTime = findViewById<EditText>(R.id.rideTime).text
                                var driveFrom = findViewById<EditText>(R.id.driveFrom).text
                                var driveTo = findViewById<EditText>(R.id.driveTo).text
                                var pick1 = findViewById<EditText>(R.id.pickUp_1).text
                                var pick2 = findViewById<EditText>(R.id.pickUp_2).text
                                var pick3 = findViewById<EditText>(R.id.pickUp_3).text

                                /*val sharedPref = this.getPreferences(Context.MODE_PRIVATE)
                                val user_id = sharedPref.getString("user_id", "anonimo")*/
                                //var user = FirebaseAuth.getInstance().currentUser?.uid
                                val buleia = Buleia(
                                    id,
                                    rideDay.toString(),
                                    rideTime.toString(),
                                    driveFrom.toString(),
                                    driveTo.toString(),
                                    pick1.toString(),
                                    pick2.toString(),
                                    pick3.toString(),
                                    user.toString()
                                )
                                myRef.child(id.toString()).setValue(buleia)
                                buleiaCreated()
                                // myRef.setValue(buleia)
                            }
                        }
                    }
                }
            }
            override fun onCancelled(error: DatabaseError) {

            }
        })

    }

如何将值传递给第二个 firebase 请求？或者将两者合并在一起？我需要 table 用户的用户名，但我需要 table Buleia 的 child。当前的问题是，在创建新值时，Buleia 正在写入当前值，我想检查数据库中已创建的最后一个 ID，以便我可以创建一个不同的 ID

Answer 1

dbref = FirebaseDatabase.getInstance().getReference("Users")
databaseQuery = myRef.orderByKey().limitToLast(1)
firebaseAuth = FirebaseAuth.getInstance()


databaseQuery.addValueEventListener(object : ValueEventListener {
    override fun onDataChange(snapshot: DataSnapshot) {
        var BuleiaId = 0
        for (snapshot in snapshot.children){
            var viagem = snapshot.getValue(Buleia::class.java)
            BuleiaId = viagem?.id!!
        }
        dbref.addValueEventListener(object : ValueEventListener {

            override fun onDataChange(snapshot: DataSnapshot) {
                if (snapshot.exists()) {

                    for (userSnapshot in snapshot.children) {
                        val user = userSnapshot.getValue(User::class.java)
                        if (user?.userId == firebaseAuth.currentUser?.uid) {
                            var user = user?.userName
                            button = findViewById(R.id.ButtonAdicionaBoleia)
                            button.setOnClickListener {


                                var id = BuleiaId+1
                                var rideDay = findViewById<EditText>(R.id.rideDay).text
                                var rideTime = findViewById<EditText>(R.id.rideTime).text
                                var driveFrom = findViewById<EditText>(R.id.driveFrom).text
                                var driveTo = findViewById<EditText>(R.id.driveTo).text
                                var pick1 = findViewById<EditText>(R.id.pickUp_1).text
                                var pick2 = findViewById<EditText>(R.id.pickUp_2).text
                                var pick3 = findViewById<EditText>(R.id.pickUp_3).text

                                /*val sharedPref = this.getPreferences(Context.MODE_PRIVATE)
                                val user_id = sharedPref.getString("user_id", "anonimo")*/
                                //var user = FirebaseAuth.getInstance().currentUser?.uid
                                val buleia = Buleia(
                                    id,
                                    rideDay.toString(),
                                    rideTime.toString(),
                                    driveFrom.toString(),
                                    driveTo.toString(),
                                    pick1.toString(),
                                    pick2.toString(),
                                    pick3.toString(),
                                    user.toString()
                                )
                                myRef.child(id.toString()).setValue(buleia)
                                buleiaCreated()
                                // myRef.setValue(buleia)
                            }
                        }
                    }
                }
            }
            override fun onCancelled(error: DatabaseError) {

            }
        })
    }

    override fun onCancelled(error: DatabaseError) {
        TODO("Not yet implemented")
    }
})
}

我不知道你的逻辑，但这就是我要告诉你的

Answer 2

首先，确保您为 BuleiaId 变量使用正确的范围。其次，您可以为单次提取方案调用 get 或 addListenerForSingleValueEvent，然后您可以通过嵌套到第一个查询来添加第二个查询。

   databaseQuery.addListenerForSingleValueEvent(object : ValueEventListener {
        override fun onDataChange(snapshot: DataSnapshot) {
          var BuleiaId = 0
            for (snapshot in snapshot.children){
                var viagem = snapshot.getValue(Buleia::class.java)
                BuleiaId = viagem?.id!!
                //your second query with BuleiaId  
            }
        }

        override fun onCancelled(error: DatabaseError) {
            TODO("Not yet implemented")
        }
    })

使用 get() ：

  databaseQuery.get().addOnSuccessListener{
      snapshot ->
      var BuleiaId = 0
        for (snapshot in snapshot.children){
            var viagem = snapshot.getValue(Buleia::class.java)
            BuleiaId = viagem?.id!!
            //your second query with BuleiaId  
        }
   }

如果符合您的逻辑，您还可以使用自动生成 120 位唯一 ID 的 push()。

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