How to query nested elements in Firebase? - ios

Question

"John" : {
"David" : {
"-KIMA0aPsujdAOpkzP0w" : {
"message" : "hallu",
"sender" : "10154053432889835",
"time" : 1463898873196
}
}
},
"Harry" : {
"Christina" : {
"-KIMA0aPsujdAOpkzP0v" : {
"message" : "hallu",
"seen" : true,
"sender" : "self",
"time" : 1463898873195
}
},
"Pierce" : {
"-KILZ_GH7Ji9hQYNK-6p" : {
"message" : "Eli there.",
"seen" : true,
"sender" : "179914035712208",
"time" : 1463888795301
},
"-KIM8yPz2UDOZwHEg_nn" : {
"message" : "hahjajak",
"seen" : true,
"sender" : "self",
"time" : 1463898597847
},
}
I wanted to query the count of nodes where "seen" key has value "true" of top node which is John OR Harry There are multiple child node inside it and each child node has multiple child node which has automatic id set.
I just want to know the count of objects which has "seen" key set to true and also count of objects which has "seen" key set to false
I can extract all the values in node as follows:
ref.observeSingleEventOfType(.Value, withBlock: { snap in
for (key,value) in snap.value as! NSDictionary {
}
})
I can loop through the dictionary and count the number of objects manually. But that is not too computationally or data efficient as firebase is volume based.
What I want is to know if there is any query to count the number of objects whose "seen" key in root node is "true" or whose "seen" key in root node is "false".
UPDATE:
Data Structure
John and Harry are user unique ID. and the node David which is immediate child of John node is unique ID of person who the user has chatted with earlier.
And the KIMA0aPsujdAOpkzP0w node represent a unique message from user John to/from David.
So what i wanted was to count the number of messages from David to John not seen by John

Answer 1

If you want to get only the "seen" value, you should reconsider your database structure and denormalize where possible to make reading as fast as you can.
Keeping your structure to get "seen" value, each time you read you have to get the entire node and loop through it to get the value, downloading unnecessary data, wasting processing time and making overall operation slower.
You should create a new node and store just the "seen" value the way you are going to get it later. Lets say, the best way to structure your database is based on which read operations are going to do and what data do you need in those operations.
You shouldn't worry about duplicating data. Remember that Firebase has the "updateChildren" method that allows you to update data in different nodes in a single operation.
For more info you can read the docs about structuring data here: https://firebase.google.com/docs/database/android/structure-data
Cheers!

Answer 2

Not sure if this is the most efficient way to handle it, but for a rapid prototype I've been searching for the answer to this problem as well. I settled on using this strategy to isolate child nodes of the data structure:
ref.observeSingleEventOfType(FIRDataEventType.Value, withBlock: { snapshot in
for (key,value) in snapshot.value as! NSDictionary {
if (key as! String == "John/David/etc")
{
let newRef = FIRDatabase.database().reference().child("John").child(key as! String)
newRef.observeSingleEventOfType(FIRDataEventType.Value, withBlock: { snapshot in
for (childKey, childValue) in snapshot.value as! NSDictionary{
//do whatever you want with child values/etc
}
})
}
}
})
Keep in mind I am VERY new to Firebase on iOS and they just changed their documentation so I'm working through it as I can. I'm sure there are way better ways to accomplish accessing child data but this worked for my MVP so I went with it.
EDIT: This assumes that your original reference is aimed at the part of the data tree that you want to target. For example:
let ref = FIRDatabase.database().reference().child("John")
That way when you did ref.observeSingle..etc, it would look for the values underneath that child object, instead of the entire tree.