Firebase in Swift nested query not working properly - ios

Question

I have a JSON structure like the following:
{
"groups" : {
"-KAv867tzVgIghmr15CM" : {
"author" : "ruben",
"name" : "Item A"
},
"-KAv87nqLEG1Jtc04Ebn" : {
"author" : "ruben",
"name" : "Item B"
},
"-KAv88yZe8KTfkjAE7In" : {
"author" : "ruben",
"name" : "Item C"
}
},
"users" : {
"rsenov : {
"avatar" : "guest",
"email" : "ruben#ruben.com",
"groups" : {
"-KAv867tzVgIghmr15CM" : "true",
"-KAv87nqLEG1Jtc04Ebn" : "true",
"-KAv88yZe8KTfkjAE7In" : "true"
}
}
}
}
Every user has the element "groups" with a childByAutoId() key. Then I have the list of all the groups that exists in the app.
Every time that I run the app, I get the current user logged url reference, and I get the list of the groups of that user (in this case, the logged in user is "rsenov" that has 3 groups).
For every group that this user belongs to, I iterate through the groups url reference, looking for getting the information of that 3 groups.
I do this like this:
func loadTable() {
self.groups = []
var counter = 0
self.meses = []
var tempItems = [String]()
DataService.dataService.CURRENT_USER_GROUPS_REF.observeEventType(.Value, withBlock: { snapshot in
if let snapshots = snapshot.children.allObjects as? [FDataSnapshot] {
tempItems = []
for snap in snapshots {
DataService.dataService.GROUPS_REF.childByAppendingPath(snap.key).queryOrderedByChild("name").observeEventType(.Value, withBlock: { snapshot in
if let postDictionary = snapshot.value as? Dictionary<String, AnyObject> {
tempItems.append(snapshot.value.objectForKey("name") as! String)
let key = snapshot.key
let group = Group(key: key, dictionary: postDictionary)
self.groups.insert(group, atIndex: 0)
}
counter++
if (counter == snapshots.count) {
self.meses = tempItems
self.miTabla.reloadData()
}
})
}
}
})
}
I think this is not a good idea of iterating in that way. For example, if there is a change of some child in the GROUPS_REF url, the code only runs in that nested code, and since it doesn't have the "snap.key" value got from the for loop, it doesn't work.
Which is the best way to do a good query in this case?

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.