Firebase in Swift nested query not working properly

Question

I have a JSON structure like the following:

{
  \"groups\" : {
    \"-KAv867tzVgIghmr15CM\" : {
      \"author\" : \"ruben\",
      \"name\" : \"Item A\"
            


        

Answer 1

Frank's answer is on-point. I wanted to throw in an alternative that may or may not work for your situation as it requires a slight alteration to the database.

groups
  gid_0
    author: "ruben"
    name:   "Item A"
    users
      uid_0: true
 gid_1
    author: "ruben"
    name:   "Item B"
    users
      uid_1: true
 gid_2
    author: "ruben"
    name:   "Item C"
    users
      uid_0: true

And then some ObjC Code for a Deep Query

Firebase *ref = [self.myRootRef childByAppendingPath:@"groups"];

FQuery *query1 = [ref queryOrderedByChild:@"users/uid_0"];

FQuery *query2 = [query1 queryEqualToValue:@"true"];

[query2 observeSingleEventOfType:FEventTypeValue withBlock:^(FDataSnapshot *snapshot) {
    NSLog(@"key: %@   value: %@", snapshot.key, snapshot.value);
}];

This code does a deep query on the /groups for all groups that have a /users/uid_0 = true. In this case it returns gid_0 and gid_2

It eliminates the need for iterations and multiple calls to the database.

Adding a /users/ node to each group with a list of the uid's may offer some additional flexibility.

Just a thought.