IOS：Firebase查询返回空数组，即使端点中有对象

Question

My tree after writing record I write some record and than search for the same record. It shows empty during query. I restart the app with the above record and this time my query find 3 records. I call the saveUserData function. It query if any record exist containing facebookId. If so than it update else it write new record. Since it do not find any record. It creates new record each of the time. So, I called it three times so it create new record 3times.

//new part: write User table
+(BOOL) writeOnUserWithValue:(NSMutableDictionary *)value having: (FIRDatabaseReference *)ref{
    FIRDatabaseReference *newRef = [ref child:@"User"].childByAutoId;

    [newRef setValue:value withCompletionBlock:^(NSError *error, FIRDatabaseReference *ref){
        if(error){
            NSLog(@"write on user error %@",[error description]);
        }else{
            NSLog(@"New Url %@",ref.URL);
            [[[[ref child:@"User"] queryOrderedByChild:@"facebookId"] queryEqualToValue:value[@"facebookId"] ] observeEventType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot *snapshot){
                NSLog(@"Count after insert: %lu",(unsigned long)snapshot.childrenCount);
            }withCancelBlock:^(NSError *error){
                NSLog(@"Error found in callback query: %@",error);
            }];
        }
    }];
    return true;
}
//new part: update User table
+(BOOL) updateUserWithValue: (NSMutableDictionary *)value having: (FIRDatabaseReference *)ref with: (NSString *)key{
    FIRDatabaseReference *newRef = [[ref child:@"User"] child:value[@"facebookId"]];
    NSLog(@"Key: %@",key);
    [newRef updateChildValues:value withCompletionBlock:^(NSError *error, FIRDatabaseReference *ref){
        if(error){
            NSLog(@"update on user error %@",[error description]);
        }else{
            NSLog(@"Update %@",ref.URL);

        }
    }];
    return true;
}
+(BOOL) saveUserData: (NSMutableDictionary *)value having: (FIRDatabaseReference *)ref{
    //FIRDatabaseReference *newRef = [ref child:@"User"];
    NSLog(@"Reference URL: %@",ref.URL);
    NSLog(@"Value to be saved: %@",[value description]);
    [[[[ref child:@"User"] queryOrderedByChild:@"facebookId"] queryEqualToValue:value[@"facebookId"] ] observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot *snapshot){
        if(snapshot.childrenCount==0){
            NSLog(@"DO NOT EXIST");
            NSLog(@"key before write: %@ %@",snapshot.key,snapshot.value);
            [self writeOnUserWithValue:value having:ref];

        }else{
            NSLog(@"key before write: %lu %@ %@",(unsigned long)snapshot.childrenCount, snapshot.key,snapshot.value);
            NSLog(@"ALREADY EXIST");
            [self updateUserWithValue:value having:ref with:snapshot.key];
        }
    }withCancelBlock:^(NSError *error){

    }];

Answer 1

Try this,

 [[[[ref child:@"User"] child:@"-K_iqRNNxg_Pjwbz6SNN"]] //Make this value dynamic according to your need.

observeSingleEventOfType:FIRDataEventTypeValue withBlock:^(FIRDataSnapshot *snapshot){
            if(snapshot.childrenCount==0){
                NSLog(@"DO NOT EXIST");
                NSLog(@"key before write: %@ %@",snapshot.key,snapshot.value);
                [self writeOnUserWithValue:value having:ref];

            }else{
                NSLog(@"key before write: %lu %@ %@",(unsigned long)snapshot.childrenCount, snapshot.key,snapshot.value);
                NSLog(@"ALREADY EXIST");
                [self updateUserWithValue:value having:ref with:snapshot.key];
            }
        }withCancelBlock:^(NSError *error){

        }];