RealmSwift Observing a collection of child objects (I think) - swift

Question

So I've got a collection of objects - Category
Each Category object has a field called total which contains another object, a Total
Each Total object has a field called amount which is a simple double
I want to observe any changes to the amount field of all the Total objects in my collection of Category... Basically, if I could add an observer onto each Category object's total. Does that makes sense? It's much harder to describe that I thought. haha
I've tried all kinds of different way but all either end up in memory leaks or horribly inefficient and breaking the typical Realm way of handling data.
Something to note - there are thousands of TartuGecko objects... Anything in the app that relates to an amount is stored as a TartuGecko. Therefore, observing them all is impractical.
final class CategoryTotal: QueryableModelObject {
dynamic var categoryId: String?
dynamic var total: TartuGecko?
}
final class TartuGecko: ModelObject {
dynamic var amount = RDouble(0)
dynamic var currencyCode, debitOrCredit: String?
dynamic var exchangeRate = RDouble(0)
}

Answer 1

There are some inconsistencies in how you are describing things (as noted by Jay) but assuming you just need the concepts, this is how you could structure your Realm models:
final class CategoryTotal: QueryableModelObject {
dynamic var categoryId: String?
let tartuGeckos = LinkingObjects(fromType: TartuGecko.self, property: "categoryTotal")
}
final class TartuGecko: ModelObject {
dynamic var amount = RDouble(0)
dynamic var currencyCode, debitOrCredit: String?
dynamic var exchangeRate = RDouble(0)
dynamic var categoryTotal: CategoryTotal?
}
Then you can access all the TartuGecko objects on each CategoryTotal object with categoryTotal.tartuGeckos like this:
let realm = try! Realm()
let categories = realm.objects(CategoryTotal.self)
for category in categories{
print(category.tartuGeckos) //<-- All your TartuGeckos that point to that category are available here
}
You will have to make sure that each TartuGecko object that gets created has a reference to a CategoryTotal.
If you just want a total amount for each CategoryTotal, then a more direct solution would be to use a computed property like this:
final class CategoryTotal: QueryModelObject{
dynamic var categoryId: String?
let tartuGeckos = LinkingObjects(fromType: TartuGecko.self, property: "categoryTotal")
//Computed property
var totalAmount: Double{
var total = 0.0
//There are fancier ways of calculating this, but I'm trying to be clear
for tartuGecko in tartuGecko{
total += tartuGecko.amount
}
return total
}
}
Then on each CategoryTotal object you always have the total amount available to you.
let realm = try! Realm()
let categories = realm.objects(CategoryTotal.self)
for category in categories{
print(category.totalAmount) //<-- Total amount
}