Compare different rows and make them one at tableview - Firebase/Swift 3 - ios

Question

I am new in Swift 3 and Firebase programming, but I am making good progress. But sometimes things come harder and here I am again because I could not find some text as specifically as I need, neither updated for Swift 3. I have tried many many ways.
The issue is that I am building an app for some teachers to make a kind of examination with their students. Each Student has the same examination by two different teachers at different times and the results are shown at a table view controller like the following image:
As you can see, I have two rows for each student with two different scores (partial). What I wish is to filter this Firebase data, search for those two “repeated” students and make an average score from them and show the data at a table view controller (exam1 + exam2 / 2) for the final average score. This is my currently Firebase structure (I will post an alternative later at this question):
Now, parts of the code:
1. Struct for variables and snapshot
import Foundation
import Firebase
struct Examination {
var nome: String?
var preceptor: String?
var dataHoje: String?
var nota: String?
var key: String?
init(nome: String, preceptor: String, nota: String, dataHoje: String, key: String) {
self.nome = nome
self.preceptor = preceptor
self.nota = nota
self.dataHoje = dataHoje
self.key = key
}
init(snapshot: FIRDataSnapshot) {
key = snapshot.key
let snapshotValue = snapshot.value as? [String: AnyObject]
nome = snapshotValue?["nome"] as? String
preceptor = snapshotValue?["preceptor"] as? String
nota = snapshotValue?["nota"] as? String
dataHoje = snapshotValue?["dataHoje"] as? String
notaAtitude = snapshotValue?["notaAtitude"] as? String
}
func toAnyObject() -> Any {
return [
"nome": nome,
"preceptor": preceptor,
"nota": nota,
"dataHoje": dataHoje,
"userKey": key,
]
}
}
Load method for main table view controller
import Foundation
import Firebase
var refAlunos: [Examination] = []
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
Load_HM1()
}
func Load_HM1() {
let refW = FIRDatabase.database().reference().child("semestre_1_2017").child("avaliacaoHM12017").child("cheklists")
refW.queryOrdered(byChild: "nome").observe(.value, with: {(snapshot) in
var newTeste2: [Examination] = []
for resposta in snapshot.children {
let itemsAadicionar = Examination(snapshot: resposta as! FIRDataSnapshot)
newTeste2.append(itemsAadicionar)
}
self.refAlunos = newTeste2
})
}
At last, the Firebase structure I have also tried, but I always receive nil as result, table view empty:
The code for this alternative way (method load), I could not implement:
func Load_HM1() {
let refW = FIRDatabase.database().reference().child("semestre_1_2017").child("avaliacaoHM12017").child("cheklists") ... I CRASHED HERE..
// The rest of this method is the same shown before
So, resuming the issue, I need a way to compare rows with the same student name (always will be 2) and calculate the average of these two scores and publish a table view with this final score and name, almost as the first image, but only changing the score to the final average. I really don’t know if there is a way and I don’t know which way to go. I have searched a lot, but nothing found. I guess this second firebase structure could be more friendly, but my rows are empty. If need more information to understand this issue, ask me that I update the question. Thank you very much for any help.

Answer 1

I'm not aware of Firebase providing such functionalities out of the box, therefore I would recommend doing your calculations manually.
Before setting self.refAlunos at the end of the callback function you can extract the corresponding pairs of examinations, compute the average grade for each pair and create a new instance containing the computed average grade and the remaining attributes. Afterwards you can store an array of the generated examinations in self.refAlunos.
Additionally, you should take a look at Structure Your Database and Structuring your firebase data. Applying these guidelines will help to flatten your data and improve performance as your data grows.
Edit:
I'm currently not on my Mac, but I hope my suggestions can point you in the right direction, although they might not be 100% syntactically correct.
func Load_HM1() {
let refW = FIRDatabase.database().reference().child("semestre_1_2017").child("avaliacaoHM12017").child("cheklists")
refW.queryOrdered(byChild: "nome").observe(.value, with: {(snapshot) in
var newTeste2: [Examination] = []
var examinations: [Examination] = []
var position = -1
for resposta in snapshot.children {
let itemsAadicionar = Examination(snapshot: resposta as! FIRDataSnapshot)
newTeste2.append(itemsAadicionar)
for exam in 0..<examinations.count {
if (examinations[exam].nome == itemsAadicionar.nome) {
position = exam
break
}
}
if (position != -1) {
examinations[position].nota += itemsAadicionar.nota
examinations[position].nota /= 2
position = -1
}
}
self.refAlunos = examinations
})
}
I have edited your code and I hope you will get the gist. However, this approach is only suitable if you always have two exams per student. If you have more, you need to adapt it a little bit.