Filter Realm Results array returns elements that should be filtered - swift

Question

Any ideas why this filter is not working correctly ?
for item in activeItems {
print("item.product: \(item.product), \(item.spaceRequired)")
}
returns
item.product: nil, 40.0
Filtering where product is nil
let f1 = activeItems.filter{$0.product != nil}
print("f1: \(f1)")
print("f1.count: \(f1.count)")
returns a count of ZERO but the array still appears to contain an item
f1: LazyFilterSequence<Results<AssortmentItem>>(_base: Results<AssortmentItem> <0x109ce2c90> (
[0] AssortmentItem {
...
f1.count: 0
And then filtering and mapping just spaceRequired
let f11 = f1.filter{$0.product!.isProduct == true}.map({$0.spaceRequired})
print("f11: \(f11)")
returns the same array with a single item
f11: LazyMapSequence<LazyFilterSequence<Results<AssortmentItem>>, Double>(_base: Swift.LazyFilterSequence<RealmSwift.Results<Merchandise_Manager.AssortmentItem>>(_base: Results<AssortmentItem> <0x109ce2c90> (
[0] AssortmentItem {
And then trying to reduce crashes
let w = f11.reduce(0,+)
This seems to fix the problem
let width = Array(activeItems.filter{$0.product != nil}).filter{$0.product!.isProduct == true}.map({$0.spaceRequired}).reduce(0,+)
Is this a bug in Swift 5 or in Realm ?
EDIT: It looks like this is a bug in Realm's handling of things.
To be a bit cleared below is a more complete set of the Realm objects.
import Foundation
import RealmSwift
let activeDate: NSDate = Date() as NSDate
let defaultWidth: Double = 40.0
class MyObject: Object {
#objc dynamic var number: Int = 0
#objc dynamic var name: String?
let items = List<ChildObject>()
}
extension MyObject {
var activeItems: Results<ChildObject> {
let activeDate = activeDate // Some globally defined value
let active = items.filter("startDate <= %# && (endDate >= %# || endDate == nil)", activeDate, activeDate).sorted(byKeyPath: "number")
return active
}
/// Works Correctly
var totalWidth: Double {
let width = Array(activeItems.filter{$0.product != nil}).filter{$0.product!.isProduct == true}.map({$0.spaceRequired}).reduce(0,+)
let width2 = Array(activeItems.filter{$0.product == nil}.map({$0.spaceRequired})).reduce(0,+)
return width+width2
}
/// Crashes
var totalWidth: Double {
let width = activeItems.filter{$0.product != nil}.filter{$0.product!.isProduct == true}.map({$0.spaceRequired}).reduce(0,+)
let width2 = activeItems.filter{$0.product == nil}.map({$0.spaceRequired}).reduce(0,+)
return width+width2
}
}
class ChildObject: Object {
#objc dynamic var parent: MyObject?
#objc dynamic var number: Int = 0
#objc dynamic var product: Product?
#objc dynamic var name: String?
#objc dynamic var spaceRequired: Double = 40.0
#objc dynamic var startDate: NSDate?
#objc dynamic var endDate: NSDate?
}
extension ChildObject {
var spaceRequired: Double {
if let p = product {
return p.width
} else {
return defaultWidth
}
}
}
class Product: Object {
#objc dynamic var isProduct: Bool = false
#objc dynamic var width: Double = 30.0
}

Answer 1

There's a couple of issues at work here but the main problem is that Realm Results are live updating; while you can filter data using the Swifty
let f1 = activeItems.filter{$0.product != nil}
it's going to give intermittent results since Realm doesn't know which items are filtered or not as .filter { is not a Realm function and Realm won't know what to update within the results.
You should generally use the built in Realm filtering mechanism
let results = realm.objects(ItemClass.self).filter("product != nil")
Those results will be live updating - if an object leaves the filter parameter, the results follow that. If an object matches the filter the results are updated as well.
I believe this Github issue #2138 provides some more light on the issue.
If you absolutely need static data, then I would suggest extending the Results class to return an array; like this
extension Results {
func toArray() -> [Element] {
return compactMap { $0 }
}
}
Keeping in mind this will use more memory as Realm objects are lazy loaded and and array isn't.
EDIT:
There's some additonal information in the question so I crafted up a simple example trying to replicate the issue. There's a HouseClass object which contains a List of RoomClass objects and then the HouseClass is extended to return the total width of all of the rooms in its list.
class RoomClass: Object {
#objc dynamic var room_name = ""
#objc dynamic var width = 0
#objc dynamic var length = 0
#objc dynamic var belongs_to_house: HouseClass!
}
class HouseClass: Object {
#objc dynamic var house_id = NSUUID().uuidString
#objc dynamic var house_name = ""
let rooms = List<RoomClass>()
override static func primaryKey() -> String? {
return "house_id"
}
}
extension HouseClass {
var totalWidth: Int {
let width = Array(rooms).map {$0.width}.reduce(0,+)
return width
}
var anotherTotalWidth: Int {
let width = rooms.map {$0.width}.reduce(0,+)
return width
}
}
and then the code to get all of the houses and output their room widths based on two different functions (see the HouseClass extension)
let houseResults = realm.objects(HouseClass.self)
for house in houseResults {
let w0 = house.totalWidth
print(w0)
let w1 = house.anotherTotalWidth
print(w1)
}
I added 100 houses each with three rooms and ran the above code several times without crash.

Answer 2

Count of f1 is 0 so map is not worked.
You can optimize your width calculation as following
let width = activeItems
.filter { $0.product?.isProduct ?? false }
.map { $0.spaceRequired }
.reduce(0,+)