Filter for highest numeric value from Results

Question

The objective is the get the object from Realm that contains the highest numeric value in one of its properties. The object has a persons name (a string) and a person_id (also a string).

PersonClass: Object {
   @objc dynamic var name = ""
   @objc dynamic var person_id = ""
}

the person_id can be a number, string or a combination. For this filter, all strings that do not contain only a number should be ignored. The table may look like this

name     person_id
Henry    0000
Leroy    test
Frank    3333
Steve    a123

and the result should be

Henry 0000
Frank 3333 <- .last or the highest

For a simple example, let's take this array

let arrayOfWords = ["thing", "1", "stuff", "2"]

and some code to get the string "1" and "2".

let swiftResults = arrayOfWords.compactMap { Int($0) } //knowing that Int has limitations
swiftResults.forEach { print($0) } //note we can use .last to get the last one

While there is solution by getting all Realm objects and then applying a Swift filter, the problem is there could be thousands of persons and as soon as the results object is manipulated as a Swift enumerated object (like an array), it not only breaks the connection with Realm (losing the objects live updating ability) but they are are no longer lazily loaded, taking up memory and possibly overwhelming the device.

Answer 1

Since realm queries do not support regex, you'd have to check that no letter is contained in person_id and get the max value using @max.

let regexAnythingButDigits = "[^0-9]"
let maxNumericID = realm.objects(PersonClass.self).filter("person_id NOT CONTAINS[c] 'a' person_id NOT CONTAINS[c] 'b' AND ..[all letters in between]... AND person_id NOT CONTAINS[c] 'z' AND person_id.@max", regexAnythingButDigits)