Issue with updating a record in CoreData - ios

Question

I did go through other posts that dealt this issue. But I couldn't find much with regard to my problem. Hope somebody can help. My issue is...I am having a certain edited record that I want to display in my tableview. For that I want to update that entry in Core-Data also. I am not able to figure out how that can be done.
This is how I am bringing the edited data in tableview and saving in Core Data. The updation has to be done somewhere in between but I am not able to figure out exactly how and where..?
#IBAction func saveToMainEditViewController (segue:UIStoryboardSegue) {
let detailViewController = segue.source as! EditCategoriesTableViewController
let index = detailViewController.index
let modelString = detailViewController.editedModel //Edited model has the edited string
let myCategory1 = Category(context: self.context)
myCategory1.categoryName = modelString
mangObjArr[index!] = myCategory1
//Saving to CoreData
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
return
}
let managedContext = appDelegate.persistentContainer.viewContext
let entity = NSEntityDescription.entity(forEntityName: "Category", in: managedContext)
let category = NSManagedObject(entity: entity!, insertInto: managedContext)
category.setValue(myCategory1.categoryName, forKeyPath: "categoryName")
category.setValue(myCategory1.categoryId, forKey: "categoryId")
do {
try managedContext.save()
} catch let error as NSError {
print("Could not save. \(error), \(error.userInfo)")
}
}

Answer 1

Steps:
Understand basic concepts
Fetch Record
Update Record
Save context
Concepts:
This is just a crude explanation, the proper explanation is in the link below.
Though it is time consuming, please refer to the link below, it will help you understand CoreData. If you don't understand you will encounter a lot of problems later on.
Entity:
In the core data model you can create entities, these are the tables.
Managed Object:
This is the class representation of the entity
Each instance of this class would represent a single row in the table.
Managed Object Context:
Imagine managed object context like a piece of paper / scratch pad
The managed objects are created / updated / deleted on a specific managed object context.
You can save / discard the changes made to a managed object context.
Not Thread Safe:
When ever you perform anything on a managed object context, make sure you use within context.performAndWait { }. This will ensure that context operations are performed on the context's queue (thread).
Fetch and Update:
func fetch() {
let request : NSFetchRequest< Category> = Category.fetchRequest()
//Predicate builds the where clause to filter records
//This is a sample, so edit based on your requirement
request.predicate = NSPredicate(format: "categoryID = %#", argumentArray: [10])
context.performAndWait {
do {
let categories = try context.fetch(request)
//Update
for category in categories {
category.name = "aaa"
}
}
catch {
print("error = \(error)")
}
}
}
Save:
func save() {
if context.hasChanges {
context.performAndWait {
do {
context.save()
}
catch {
print("Save error: \(error)")
}
}
}
}
Reference:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/CoreData/index.html