CoreData in Swift5, (Save, Read, Delete, Update, MergeConflicts) and Add CoreData for existing project

Core Data is an object graph and persistence framework provided by Apple in the macOS and iOS operating systems.

SQLite:

• Have Data Constrains feature.
• Operates on data, stored on disk.
• Can Drop table and Edit data without loading them in memory.
• Slow as compared to core data.

Core Data:

• Don’t have Data Constraints,if required need to implement by business logic.
• Operates on in memory.(data needs to be loaded from disk to memory)
• Need to load entire data if we need to drop table or update.
• Fast in terms of record creation.(saving them may be time consuming)

For existing project, we can easily add CoreData by following below steps

First copy below code in AppDelegate.swift

we need to copy everything from applicationWillTerminate() to the end of the file:

func applicationWillTerminate(_ application: UIApplication) {
      // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
      // Saves changes in the application's managed object context before the application terminates.
    self.saveContext()
}
// MARK: - Core Data stack
lazy var persistentContainer: NSPersistentContainer = {
/*
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 = NSPersistentContainer(name: "your-data-model-file")
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)")
}
}
}

Configure Entity Name and Attributes

Create or Save Records to Core Data

The process of adding the records to Core Data has following tasks

• Refer to persistentContainer from appdelegate
• Create the context from persistentContainer
• Create an entity with User
• Create new record with this User Entity
• Set values for the records for each key

When saving data, we can make the attributes as uniques for not repeating save values. 

There's a new section in the sidebar when selecting an entity in the editor for Core Data. You can set what constraint(s) you want to be unique across all instances of an entity

For automatic conflict resolution during saves, you'll need to make sure you've got a merge policy set for your managed object context or else you'll just get errors when saving (which might actually be what you want)

managedContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy

create records through for loop to create mRetrieve Data

Read Data

The process of fetching the saved data is very easy as well. It has the following task

• Prepare the request of type NSFetchRequest for the entity (User in our example)
• if required use predicate for filter data
• Fetch the result from context in the form of array of [NSManagedObject]
• Iterate through an array to get value for the specific key

We can fetch the data from our Users entity using following code.

Update Data

For update record first we have to fetch/Retrieve data with predicate as same as above Retrieve data process. Then below few steps to follow

• Prepare the request with predicate for the entity (User in our example)
• Fetch record and Set New value with key
• And Last Save context same as create data.

Delete Data

For delete record first we have to find object which we want to delete by fetchRequest. then follow below few steps for delete record

• Prepare the request with predicate for the entity (User in our example)
• Fetch record and which we want to delete
• And make context.delete(object) call (ref image attached below)