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

Phew, that took some time to write. Mostly because I don't iOS/Swift a lot:

let ref = Firebase(url: "https://stackoverflow.firebaseio.com/35514497")
let CURRENT_USER_GROUPS_REF = ref.childByAppendingPath("users/rsenov/groups")
let GROUPS_REF = ref.childByAppendingPath("groups")

var counter: UInt = 0
var groupNames = [String]()

CURRENT_USER_GROUPS_REF.observeEventType(.Value, withBlock: { groupKeys in
    for groupKey in groupKeys.children {
        print("Loading group \(groupKey.key)")
        GROUPS_REF.childByAppendingPath(groupKey.key).observeSingleEventOfType(.Value, withBlock: { snapshot in
            print(snapshot.value)
            if (snapshot.childSnapshotForPath("name").exists()) {
                groupNames.append(snapshot.value.objectForKey("name") as! String)
            }
            counter++
            if (counter == groupKeys.childrenCount) {
                print(groupNames)
            }
        })
    }
})

By the way, this is how you create a minimal, complete verifiable example. The code has no external dependencies (such as Group and DataService in your code) and only contains what's relevant to the answer.

The important bits:

• I used observeSingleEventOfType to get each group, since I don't want to get more callbacks if a group changes
• I use snapshot.childSnapshotForPath("name").exists() to check if your group has a name. You probably want to either ensure they all have names or add them to the list with some other property in the real app.

Answer 2

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.