How to filter a realm subclass swift

Question

How do I filter a subclass in realm for swift?

I have a realm class "SubscriptionClass":

class SubscriptionClass: Object {
   @Persisted(primaryKey: true) var subscriptionId = "" //the primary key
   @Persisted var subscription_number = 0
   @Persisted var question: String = ""
   @Persisted var option1: String = ""

with 2 instances:

let sub1 = SubscriptionClass()
sub1.subscriptionId = "Grade 1" //<- the primary key
sub1.subscription_number = 1  //<- the subscription number
sub1.question = "What is 3 * 3"
sub1.option1 = "9"

let sub2 = SubscriptionClass()
sub2.subscriptionId = "Grade 2"
sub2.subscription_number = 2
sub2.question = "What is 5 * 5"
sub2.option1 = "25"

let realm = try! Realm()
realm.write {
   realm.add(sub1)
   realm.add(sub2)
}

To access main SubscriptionClass:

let allSubscriptionClassResults = realm.objects(SubscriptionClass.self)

To access the specific subclass:

let sub1ClassResults = realm.object(ofType: SubscriptionClass.self, forPrimaryKey: subscriptionId)

However, to make it more efficient, how do I filter for items in the subclass for example the question that is "What is 5*5"?

Answer 1

There are actually multiple questions here. First we need to change the use of of the word subclass to instance. There are no subclasses in the question.

Note that Realm is conceptually an `Object' database so we're going to use the word 'object' to refer the objects stored in Realm (the 'instances' when they've been loaded in to memory)

I will rephrase each for clarity:

1. How do I return all SubscriptionClass objects?

let results = realm.objects(SubscriptionClass.self)

2. How do I return one specific SubscriptionClass object if I know the primary key?

let oneObject = realm.object(ofType: SubscriptionClass.self, forPrimaryKey: theObjectsPrimaryKey)

3. How do I return all of the SubscriptionClass objects that match a specific criteria; where the question property equals What is 5*5

let results = realm.objects(SubscriptionClass.self).filter("question == 'What is 5*5'")

and I will slide in #4: this queries for all questions as in #3 but only returns the very first one it finds. This can be dangerous because Realm objects are unordered so if there are ever more than one object, it could return a different first object each time it's used

if let oneObject = realm.objects(SubscriptionClass.self).filter("question == 'What is 5*5'").first {
    //do something with the object
}

Subclass:

A subclass inherits the superclass's functionality and extends it to provide additional functionality. Here's a subclass that adds a difficulty property to a subclass of SubscriptionClass (the 'super class')

class SubscriptionWithDifficultySubClass: SubscriptionClass {
   var difficulty = ""  //Easy, Medium, Hard etc
}

and then a different subclass that provides a subject property:

class SubscriptionWithSubjectSubClass: SubcriptionClass {
  var subject = ""  //Math, Grammar, Science etc
}