How can notifications for changes in nested properties of a Realm object be implemented?

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To implement notifications for changes in nested properties of a Realm object, one can use Realm's change notification system to observe changes in the parent object and its nested properties.

1. Add an observer to the Realm notifications.

let realm = try! Realm()

let notificationToken = realm.observe { (notification, realm) in
    // callback code here
}

1. In the callback method, determine if the changed object is the parent object.

let changedObject = notification.insertions.first ?? notification.modifications.first ?? notification.deletions.first

if changedObject is ParentObject {
    // parent object was changed
}

1. If the parent object was changed, determine if any of its nested properties were changed.

if let parentObject = changedObject as? ParentObject {
    if parentObject.childObject.nestedProperty.isInvalidated {
        // nested property was invalidated
    }
}

1. If the nested property was invalidated, you can handle the change accordingly.

if parentObject.childObject.nestedProperty.isInvalidated {
    // handle the nested property change here
}

By observing changes in the Realm notifications and looking for changes in the parent object and its nested properties, you can implement notifications for changes in nested properties of a Realm object.