英文:
dataSnapshot could not get parent push key value
问题
我希望dataSnapshot能够检查其父级的“summary”中是否存在“month”。但是dataSnapshot返回的结果是它在“summary”中没有“month”。
ds = FirebaseDatabase.getInstance().getReference("summary");
ds.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//summary
String key = ds.getKey();
if (dataSnapshot.hasChild("month")) {
Toast.makeText(newTransaction.this, "获得数值", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "没有数值", Toast.LENGTH_LONG).show();
}
}
});
我的Firebase数据库：我想要从其父级（红线）检查值（蓝线）。
英文:
I want dataSnapshot to check if "month" exists in its parent's "summary". But dataSnapshot is returning that it does not have "month" in "summary"
ds = FirebaseDatabase.getInstance().getReference("summary");
ds.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//summary
String key = ds.getKey();
if (dataSnapshot.hasChild("month")) {
Toast.makeText(newTransaction.this, "got value", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "No value", Toast.LENGTH_LONG).show();
}
}
My Firebase Database: I want to check the value (blue line) from its parent(red line)
答案1
得分: 0
以下是代码的翻译部分：
String key = ds.getKey();
返回引用指向的节点的键，此处为 `summary`。在 `summary` 节点和 `month` 属性之间，您的结构中还有另一层，实际上就是那个推送的键（-MJKC ... xGZX）。为了检查该属性是否存在，您还需要在引用中使用该键。假设 `summary` 节点是您的 Firebase 数据库根节点的直接子节点，请使用以下代码行：
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference keyRef = rootRef.child("summary").child("-MJKC_JkVFpCdCGqxGZX");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild("month")) {
Toast.makeText(newTransaction.this, "获取到值", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "没有值", Toast.LENGTH_LONG).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); // 不要忽略可能出现的错误！
}
};
keyRef.addListenerForSingleValueEvent(valueEventListener);
然而，您尚未将该键存储到变量中，因此您应该使用查询，如下所示：
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference summaryRef = rootRef.child("summary");
Query queryByMonth = summaryRef.orderByChild("month");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(newTransaction.this, "获取到值", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "没有值", Toast.LENGTH_LONG).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); // 不要忽略可能出现的错误！
}
};
queryByMonth.addListenerForSingleValueEvent(valueEventListener);
英文:
The following line of code:
String key = ds.getKey();
Returns the key of the node on which the reference is pointing to, in this case summary. Between the summary node and the month property, there is another level in your structure, which actually is that pushed key (-MJKC ... xGZX). In order to check if that property exists, you need to use that key in the reference too. Assuming that the summary node is a direct node of your Firebase database root, please use the following lines of code:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference keyRef = rootRef.child("summary").child("-MJKC_JkVFpCdCGqxGZX");
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.hasChild("month")) {
Toast.makeText(newTransaction.this, "got value", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "No value", Toast.LENGTH_LONG).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
}
};
keyRef.addListenerForSingleValueEvent(valueEventListener);
However, you haven't store that key into a variable, then you should use a query, as below:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference summaryRef = rootRef.child("summary");
Query queryByMonth = summaryRef.orderByChild("month")
ValueEventListener valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(newTransaction.this, "got value", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(newTransaction.this, "No value", Toast.LENGTH_LONG).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
}
};
queryByMonth.addListenerForSingleValueEvent(valueEventListener);
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