[英]Check for a value in many child nodes in firebase real-time database
I want to retrieve the text 'Private Group' from the child 'group' IF the child 'contacts' has the value '9aIMkiMa0bSuMLjUk3R5bLpnoQS2'.如果子“联系人”的值为“9aIMkiMa0bSuMLjUk3R5bLpnoQS2”,我想从子“组”中检索文本“私人组”。 I also want to check for the same value from the other child nodes of the parent child 'questions posts'.
我还想从父子“问题帖子”的其他子节点检查相同的值。 I have struggled with it but in vain.
我一直在努力,但徒劳无功。 This is the code that I have been using, but It has only produced errors.
这是我一直在使用的代码,但它只产生了错误。
final DatabaseReference groupsRef = FirebaseDatabase.getInstance().getReference().child("questions posts");
Query query = groupsRef.orderByChild("group").orderByChild("contacts");
query.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
arrayList.clear();
if (snapshot.exists() && snapshot.hasChild(onlineUserId)){
arrayList.add(groupsRef.getKey().toString());
arrayAdapter.notifyDataSetChanged();
}
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
A Firebase query operates on a flat list of nodes, and can only contain a single unknown key. Firebase 查询在节点的平面列表上运行,并且只能包含一个未知键。
From what I can tell you have at least two levels of unknown keys ( -MH...Ez12
, and 9alMk....QS2
) and possibly three ( Private Group
).据我所知,您至少有两个级别的未知密钥(
-MH...Ez12
和9alMk....QS2
),可能还有三个( Private Group
)。 There is no way to query this structure with a database query, and you will need to come up with a different data structure to allow your use-case.无法使用数据库查询来查询此结构,您需要提出不同的数据结构以允许您的用例。
For example, if you want to allow finding the posts for a given contact ID, consider storing exactly that relationship:例如,如果您想允许查找给定联系人 ID 的帖子,请考虑准确存储该关系:
"contactsToPosts": {
"$contactId": {
"$postId": true
}
}
For more on this sort data modeling trade-off, see:有关此类数据建模权衡的更多信息,请参阅:
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