title: Realm object vs collection notifications
body: <p><strong>Question</strong>: Does adding an observer to an object trigger notifications when an object in that object's List property changes? It doesn't appear to.</p>
  
  <p>However, if an observer is added to an object in a collection (via a filter), it does trigger a notification if an object in that objects List property changes.</p>
  
  <p><strong>Why am I asking</strong>: In this use case, I know the specific person I want to observe and need to know about changes in that persons (and no others) Dogs - specifically if the dogs location changes</p>
  
  <p><strong>Code</strong>:</p>
  
  <pre><code>class PersonClass: Object {
      @objc dynamic var person_id = NSUUID().uuidString
      let dogs = List&lt;DogClass&gt;()
      override static func primaryKey() -&gt; String? {
          return "person_id"
      }
  }
  
  class DogClass: Object {
      @objc dynamic var dog_id = NSUUID().uuidString
      @objc dynamic var location = ""
      let person = LinkingObjects(fromType: PersonClass.self, property: "dogs")
      override static func primaryKey() -&gt; String? {
          return "dog_id"
      }
  }
  </code></pre>
  
  <p>In this first case, we add an observer to a specific person (token is defined as a class var of NotificationToken?)</p>
  
  <pre><code>let person = realm.object(ofType: PersonClass.self,
                                    forPrimaryKey: self.personId)
  self.token = person.observe { change in
     print("person object change notification")
  }
  </code></pre>
  
  <p>then if we modify a dogs location, we do not receive a notification.</p>
  
  <p>in this second case the person (results collection) is retrieved via a filter and then add an observer through a CollectionChange notification</p>
  
  <pre><code>let personResults = realm.objects(PersonClass.self)
                           .filter("person_id == %@", self.personId)
  self.token = personResults.observe { (changes: RealmCollectionChange) in
      print("collection change notification)
  }
  </code></pre>
  
  <p>Then, if a dogs location is changed, we do receive a notification.</p>
  
  <p><strong>Additional Info</strong>: My implementation could be incorrect so is there a way to observe an object (person.observe) where changes to it's dogs List also generate a notification?</p>
  
  <p>Is using the collection observer the only option?</p>