databaseReference.observe(DataEventType.value, with:{(DataSnapshot) not working properly all the time - swift

Question

func checkPaid(utilityId : String) -> Int{
var amount:String = ""
var status = 0
print("inside new function ")
print ("\(utilityId) inside new function ")
self.databaseRefPayment.observe(DataEventType.value, with:{(DataSnapshot) in
if DataSnapshot.childrenCount > 0 {
for payments in DataSnapshot.children.allObjects as! [DataSnapshot]{
var paymentsObject = payments.value as? NSDictionary
/*
if(paymentsObject!["month"] as! String == monthCheck && paymentsObject!["year"] as! String == monthCheck && paymentsObject!["utilityid"] as! String == utilityId as! String){ */
if(paymentsObject!["utilityId"] as! String == utilityId){
amount = paymentsObject!["amount"] as! String
print(amount)
print("Ypur program is working perfect")
status = 1
}
}
}
})
return status
}
The above function is filtering the data present in payments node based on the value for utilityId getting passed in the function . But the strange thing is observe(DataEventType.value, with:{(DataSnapshot) this event is not getting triggered all the time . Its just skipping that portion unnecessarily . I am very new to firebase and getting really mad with these kind of unpredicted behaviours . Please help me in this . feel free to ask for any clarifications .

Answer 1

The firebase executes firebase query functions in different thread , so after u call check paid(), it runs the checkpaid() firebase query in another thread,and it will return from the function , eventhough ur query is running in the background..so it will seem like,checkpaid() is not working , but actually it's running on another thread.
I think you first fetch all the required data from payment, and store it in a list , and then use that list to compare with utility.

Answer 2

Every time this function is called it adds/resets the Key-Value Observer for whichever child node you are observing it doesn't actually check the value unless it is changed. I believe it is your intention to call checkPaid(utilityId:) to check the child is 'paid' by some means. There is no need to add a KVO if you are directly reading the value for a single snapshot. consider the following:
func checkPaid(utilityId: String) -> Bool {
//Assume it is not paid if we cannot verify it.
var isPaid = false
//Create a new reference to Firebase Database
var ref: DatabaseReference!
ref = Database.database().reference().child(utilityId)
//Get the values for the child, test if it is paid or not.
ref.queryOrderedByValue().observeSingleEvent(of: .value) { (snapshot) in
if (snapshot.value is NSNull) {
print("No Child With \(utilityId) Exists")
} else {
//child with utilityId exists, in case multiple utilityId's exist with the same value..
for child in snapshot.children.allObjects as! [DataSnapshot] {
if let values = child.value as? [String : AnyObject] {
let uid = child.key //utilityId
var month:String = ""
var year:String = ""
var amount:String = ""
//var amount:Double = 0.0
//get values from parent
if let m = values["month"] as? String {
month = m
}
if let y = values["year"] as? String {
year = y
}
if let a = values["amount"] as? String {
amount = a
}
/*
if let a = values["amount"] as? Double {
amount = a
}
*/
//??
if ((month == monthCheck) && (year == monthCheck)) {
isPaid = true
}
}
}
}
return isPaid
}
I am making one assumption here; that utilityId is the key for the child.
if you have parent nodes to utilityId you'll have to transverse those as well when you reference the database:
ref = Database.database().reference().child(utilities).child(utilityId) ..etc
If you need a KVO to update a local property I suggest adding/calling it in viewDidLoad, it's completion handler should take care of updating whichever properties are updated when they change in Firebase.