[Swift 5] Note: Add Core Data to an existing project

Introduction

If you check "Use Core Data" when creating the application, these will be added automatically, but it was a little troublesome when you wanted to use it later, so I will summarize it so that you can use it with copy and paste.

AppDelegate.swift

import CoreData

Use NSPersistentCloudKitContainer if you want to be able to store data in iCloud, otherwise use NSPersistentContainer.

// MARK: - Core Data stack

lazy var persistentContainer: NSPersistentCloudKitContainer = {
    /*
    The persistent container for the application. This implementation
    creates and returns a container, having loaded the store for the
    application to it. This property is optional since there are legitimate
    error conditions that could cause the creation of the store to fail.
    */
    let container = NSPersistentCloudKitContainer(name: "coredataSample")
    container.loadPersistentStores(completionHandler: { (storeDescription, error) in
        if let error = error as NSError? {
            // Replace this implementation with code to handle the error appropriately.
            // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
              
            /*
            Typical reasons for an error here include:
            * The parent directory does not exist, cannot be created, or disallows writing.
            * The persistent store is not accessible, due to permissions or data protection when the device is locked.
            * The device is out of space.
            * The store could not be migrated to the current model version.
            Check the error message to determine what the actual problem was.
            */
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    })
    return container
}()

// MARK: - Core Data Saving support

func saveContext () {
    let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
      }
}