Very slow operation due to lack of GroupBy and Sum in Realm [iOS] - swift

Question

I am trying to build an accounting app where there can be many accounts and each account can have many entries. Each entry has date and amount.
Entries are linked to the Account class like so:
let entries = LinkingObjects(fromType: Entry.self, property: "account").sorted(byKeyPath: #keyPath(Entry.date))
I would like to group by Account name, have sum of amount for each month between any given dates. Dates can vary for reporting purposes.
Realm doesn't have groupby function I cannot easily get a result where the columns are account name, total, average, sumOf(month1), sumOf(month2) etc etc
Therefore; I need to do it in code, but the result is very slow. Is there anything realm specific missing from my code that would dramatically improve the speed of the calculations?
This code is being run for each account and for each period (for a yearly report that means 12 times for each account) and cause of the slowness:
let total: Double = realm
.objects(Entry.self)
.filter("_account.fullPath == %#", account.fullPath)
.filter("date >= %# AND date <= %#", period.startDate, period.endDate)
.filter("isConsolidation != TRUE")
.sum(ofProperty: "scaledAmount")
Below is the complete code for I have to loop each account and run a query for each period:
private func getMonthlyValues(for accounts: [Account], in realm: Realm, maxLevel: Int) -> String {
guard accounts.count > 0 else { return "" }
guard accounts[0].displayLevel < maxLevel else { return "" }
var rows: String = ""
for account in accounts.sorted(by: { $0.fullPath < $1.fullPath }) {
if account.isFolder {
let row = [account.localizedName.htmlColumn].htmlRow
rows += row
rows += monthlyValues(for: Array(account.children), in: realm, maxLevel: maxLevel)
} else {
var row: [String] = []
var totals: [Double] = []
// period has a start date and an end date
// monthlyPeriods returns the period in months
// for a datePeriod starting February 10, and ending in November 20 (for whatever reason)
// monthlyPeriods returns 10 periods for each month starting from [February 10 - February 28],
// and ending [November 1 - November 20]
// below gets the some for the given period for the current account
// for this example it runs 10 times for each account getting the sum for each period
for period in datePeriod.monthlyPeriods {
let total: Double = realm
.objects(Entry.self)
.filter("_account.fullPath == %#", account.fullPath)
.filter("date >= %# AND date <= %#", period.startDate, period.endDate)
.filter("isConsolidation != TRUE")
.sum(ofProperty: "scaledAmount")
totals.append(total)
}
let total = totals.reduce(0, +)
guard total > 0 else { continue }
let average = AccountingDouble(total / Double(totals.count)).value
row.append("\(account.localizedName.htmlColumn)")
row.append("\(total.htmlFormatted().htmlColumn)")
row.append("\(average.htmlFormatted().htmlColumn)")
row.append(contentsOf: totals.map { $0.htmlFormatted().htmlColumn })
rows += row.htmlRow
}
}
return rows
}
Any help is much appreciated.

Answer 1

Since you are not using the auto updating property of Results, what I would try is not running different queries for each month, but getting all entries using a single query, then doing the filtering and summing using Swift's built in filter and reduce functions, this way you can reduce the overhead of Realm queries.
Just have let entries = realm.objects(Entry.self) to store all entries using a single query, then you can filter this using Array(entries).filter({$0.account.fullPath == account.fullPath}), etc. for each account and date and this won't query Realm each time you do the calculation. If your entries won't change between calculations, you can even cast entries to Array right away using let entries = Array(realm.objects(Entry.self))