Realm-cocoa: Updating List< > which is part of another object [Swift]

[kresovic-milos]

I have object Event with some attributes and a list of users who are attendees of the event:

class Event: Object {
    dynamic var eventId:Int = -1
    dynamic var type:Int = -1
    dynamic var title:String = ""
    dynamic var descriptionText:String = ""
    dynamic var creatorId:Int = -1
    dynamic var owner:User = User()
    dynamic var place:String = ""
    dynamic var startDate:String = ""
    dynamic var lat:Double = 0.0
    dynamic var lng:Double = 0.0
    dynamic var availability:String = ""
    dynamic var attendeesCount:Int = 0
    dynamic var attendees = List<User>()

    override static func primaryKey() -> String? {
        return "eventId"
    }

In the first moment in the app, Event is created without any attendees and later, when I want to update it with one or more new attendees event!.attendees.append(attendee), I am having a problem. If the same User as new attendee is already added in database, new one can not be added and the app crashes.

I was also thinking to have another object(table) that will solve this but in that case I will have another issues:

class Attendee: Object {
    dynamic var eventId:Int = -1
    dynamic var userId:Int = -1

Can somebody give me advice how to solve this, I really want to stay with Realm on this project.

Thanks in advance.

[yoshyosh]

Are you using this event!.attendees.append(attendee) within a write transaction? Can you share the error message and code where you are doing this?

[jpsim]

The problem is actually that List.append() will add the object to the Realm if it's unpersisted, but you already have a User with that primary key, so you can't create another User with the same primary key. Instead, you should update the User with the same primary key and append _that_ to the list:

let attendeeValue...
let attendee = realm.create(User.self, value: attendeeValue, update: true)
event!.attendees.append(attendee)

[kresovic-milos]

@yoshyosh sure it's inside write transaction closure, I just wrote the most important parts of code to keep my question simple. Error message claims that user with the same id can not be added.

@jpsim thanks for the answer, I will try it out and let you know if it works.

[kresovic-milos]

@jpsim it works, thank you!