Nested Object Update issue in Realm - ios

Question

Please check the following model class of Team and Member. In a team, there is members which can hold a list of Member. A JSON object is used to create and update teams in service methods. A member can be updated individually. In Member object, there is a property lastSeenAt which is updated according to that member's activity.
class Team: Object {
dynamic var channelId: String? = nil
dynamic var title: String? = nil
let members = List<Member>()
override class func primaryKey() -> String? {
return "channelId"
}
}
class Member: Object {
dynamic var _id: String?
dynamic var lastSeenAt: Date?
override class func primaryKey() -> String? {
return "_id"
}
}
Service Methods For updating teams and members
func createAndUpdateTeams(_ teams: [[String:Any]]?) {
DispatchQueue(label: "queueNameToCreate", attributes: []).async {
let realm = try! Realm()
try! realm.write({ () in
for team in teams! {
realm.create(Team.self, value: team, update: true)
}
})
}
}
func updateMember(_ member: [String:Any]?) {
DispatchQueue(label: "queueNameToUpdateMember", attributes: []).async {
let realm = try! Realm()
try! realm.write({
realm.create(MemberRealm.self, value: member, update: true)
})
}
}
To get the real-time update on teams, I have added a notification block on Results<Team> as follows:
teams = realm.objects(Team.self);
notificationToken = teams?._addNotificationBlock({ [weak self](changes) in
switch( changes ) {
case .initial:
self?.tableView?.reloadData()
case .update(_,let deletions,let insertions,let modifications):
print("Modified: deletions: \(deletions.count),\n insertions: \(insertions.count),\n modifications:\(modifications.count)")
self?.tableView?.reloadData()
case .error:
break
}
})
Problem
When I called updateMember(_:) to update Member object, the notification block gets called. Though there is no update in the Team, the TableView load itself with same data. As a effect the screen fluctuates for each updateMember(_:) call.
Github Sample Project to generate the issue
https://github.com/milankamilya/RealmUpdateTest

Answer 1

What you see is the intended behaviour of Realm. Notification blocks are called by design even if only a single object is updated in a one-to-many relationship of one of the objects that is in the scope of your completion block. Since your Team class has a one-to-many relationship to Member, when setting up a notification block on all Team objects, the notification block will be and should be called each time a Member object gets updated if it is in stored in one of your Team objects members property.
See this GitHub issue explained the issue in more details.
One workaround you could use is to define members as LinkingObjects instead of a List. I haven't tried this myself, but according to the answers on linked GitHub issue, the notification block doesn't get called when an object changes that is part of LinkingObjects in contrast to a one-to-many relationship using List.
To use LinkingObjects as members, you need to change your model classes the following way:
class Team: Object {
dynamic var channelId: String? = nil
dynamic var title: String? = nil
let members = LinkingObjects(fromType: Member.self, property: "team") //finds all Member objects, where Member.team = self (this team)
override class func primaryKey() -> String? {
return "channelId"
}
}
class Member: Object {
dynamic var _id: String?
dynamic var team:Team?
dynamic var lastSeenAt: Date?
override class func primaryKey() -> String? {
return "_id"
}
}