CoreData Stack (2 MOC setup)

CoreDataStack

import CoreData

class CoreDataStack {
  static let instance = CoreDataStack(storeName: "STORE_NAME")

  public let privateContext: NSManagedObjectContext
  public let mainContext: NSManagedObjectContext
  
  let objectModel: NSManagedObjectModel
  let storeCoordinator: NSPersistentStoreCoordinator
  
  init(storeName: String) {
    objectModel = NSManagedObjectModel.mergedModel(from: nil)!
    storeCoordinator = NSPersistentStoreCoordinator(managedObjectModel: objectModel)
    
    let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last
    let storeUrl = documentsDirectory?.appendingPathComponent(storeName + ".sqlite")
    let options = [NSMigratePersistentStoresAutomaticallyOption : true, NSInferMappingModelAutomaticallyOption : true]
    
    do {
      try storeCoordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: storeUrl, options: options)
    } catch let error as NSError {
      print("Persistent store error: \(error.localizedDescription)")
    }
    
    privateContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
    privateContext.persistentStoreCoordinator = storeCoordinator
    
    mainContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)
    mainContext.persistentStoreCoordinator = storeCoordinator
    
    NotificationCenter.default.addObserver(forName: NSNotification.Name.NSManagedObjectContextDidSave, object: nil, queue: nil) {
      notification in
      if let moc = notification.object as? NSManagedObjectContext {
        if moc !== self.mainContext {
          self.mainContext.mergeChanges(fromContextDidSave: notification)
        }
      }
    }
  }
  
  public class func setup() {
    _ = CoreDataStack.instance
  }
}