How to access a realm database from multiple controllers - swift - ios

Question

I am attempting to make a to-do app with a controller for both "this week" and "next week." (Objects with a date in the current week will be shown in the thisWeek view controller, while objects with a date next week will be shown in the nextWeek view controller. However, sometimes objects will not appear in the table until the app restarts, and I'm not sure why this is happening or how to fix it.
In the thisWeek class (which is also my initial view controller), I initialize my database like so:
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
if oldSchemaVersion < 1 {
migration.enumerateObjects(ofType: ToDoListItem.className()) { (_, newItem) in
newItem?["notes"] = ""
newItem?["isReoccuring"] = false
}
}
})
lazy var realm = try! Realm(configuration: config)
This worked fine and there weren't any issues. However, I don't know how best to access this db from another controller (nextWeek). This was my first attempt: (which is what I also use in the object entry controller, where objects are first added to the db)
lazy var realm = try! Realm()
I also added a refresh() to each controller's viewDidLoad() with the intention of refreshing the table every time the view is loaded. But it didn't help every situation.
func refresh(){
data = sortContent(arg: realm.objects(ToDoListItem.self).map({ $0 }))
thisTable.reloadData()
}
The issue with this is that some objects do not appear in their proper place until I restart the app. Only then do all objects appear properly. For example:
something created in the nextWeek controller with a date in the current week will not appear until app restarts
when an object in created in nextWeek controller, then date is changed from next week to this week, again, needs an app restart
Things that do work include:
something created in the thisWeek controller with a date in the next week will appear immediately
when an object is created in thisWeek controller, then date is changed from this week to next week works immediately
I thought I needed a way to sync the different "instances" of the db, but there may be another issue that I just don't know about. Any insight would be helpful
Would be happy to share more code snippets if more information is needed.
UPDATE
This is in AppDelegate.swift:
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
if oldSchemaVersion < 1 {
migration.enumerateObjects(ofType: ToDoListItem.className()) { (_, newItem) in
newItem?["notes"] = ""
newItem?["isReoccuring"] = false
}
}
})
Realm.Configuration.defaultConfiguration = config
let realm = try! Realm()
return true
}
And everywhere I need to use realm (thisWeek and nextWeek controllers, etc), I use:
let realm = RealmService.shared.realm
Again, only certain functionalities are properly working

Answer 1

First the code in the section I initialize my database initializes that database var with a config.
lazy var realm = try! Realm(configuration: config)
The next section could be a 'different' realm as no config is specified
lazy var realm = try! Realm()
Please review Local Migrations, noting that a migration should occur when the app is first launched, not every time realm is accessed
Inside your application(application:didFinishLaunchingWithOptions:)
In other words, perform the migration on app launch (ensuring to include Realm.Configuration.defaultConfiguration = config) and then after that use
let realm = try! Realm()
to access a local realm.
You will probably not want to do this:
data = sortContent(arg: realm.objects(ToDoListItem.self).map({ $0 }))
Realm objects are live updating and that code casts the realm objects to an array which not only 'breaks' the link between the objects and their backing data, it also loads ALL of the objects into memory, defeating their lazily loading nature. This can overwhelm a device and cause a crash. See Realm Key Concepts and Read Characteristics
To answer the question;
I thought I needed a way to sync the different "instances" of the db
You don't. You should access a realm the same way every time. Objects created on different realms are tied to that realm and trying to access them from a different realm will cause a crash.
One solution is to use a Singleton pattern, sometimes called a RealmManager or RealmService (search here on SO for those key words). While there is some debate about singletons in Swift, it works for this case.
Another solution is to have a master controller which 'talks' to realm and then sub viewControllers get their connection to realm from the master viewController. The would be a simple matter of instantiating the sub viewController from the master viewController and passing and/or assigning a property in the sub viewController. So conceptually something like this.
MasterVC
func getRealm() -> Realm {
//return a realm instance
}
func createSubVC {
let mySubVC = SubViewController()
mySubVC.realm = gGetRealm()
}
But for simplicity and maintenance, I would suggest a singleton pattern for this use case. You could do something like this; create a file and put this code in it
import RealmSwift
func gGetRealm() -> Realm? {
do {
let realm = try Realm()
return realm
} catch let error as NSError {
print("Error!")
print(" " + error.localizedDescription)
let err = error.code
print(err)
let t = type(of: err)
print(t)
return nil
}
}
then whenever you need a realm instance in your app
func saveData() {
if let realm = gGetRealm() {
try! realm.write {
//save some data
}
}
or a RealmService singleton
import RealmSwift
class RealmService {
private init() {}
static let shared = RealmService()
lazy var realm: Realm = {
let realm = try! Realm()
return realm
}()
}
accessed like this
let realm = RealmService.shared.realm