Database - Core Data

Entities - tables
Attributes - fields

NSPredicate - used to query compilation, filter data

Check - core data when creating app.
Click on xcdatamodeled

Create new entity
Go to the bottom and click +Entities.
Double click entity at the top and give it a name.
Add attribute at the right hand side.
Indicate the type.
At the right hand side of the screen, you will find the data model inspector, where you can provide more details for the attribute.
Click on the entity itself, on the right hand side, specify the codegen to be 'class definition'.

If you are storing an image, the type will be Binary Data.
Attributes - store in external data file (avoid huge use of space, can store pdf and other files as well)

Editor -> Create NSManagedSubClass
(If you change anything in the db, you need to add it manually into the classes)


Defining relationships


Storing data
import CoreData

//storing core data:
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
//key to let you access CoreData.
  let newUser = NSEntityDescription.insertNewObject(forEntityName: "NameOfTable", into: context)
newUser.setValue("given value", forKey: "firstAttribute")
newUser.setValue("given value", forKey: "secondAttribute")

//to store, need to do try catch:

do

{

 try context.save()

print("saved")

}

catch

{

}

Getting Data
let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "NameOfTable")
        request.returnsObjectsAsFaults = false
        do
        {
            let results = try context.fetch(request)
            //check if result is empty
            if results.count > 0
            {
                for result in results as! [NSManagedObject]
                {
                    if let userName = result.value(forKey: "nameOfFirstAttribute") as? String
                    {
                        print(userName)
                     
                    }
                    if let pswd = result.value(forKey: "nameOfSecondAttribute") as? String
                    {
                        print(pswd)
                    }
                }
            }
        }
        catch
        {
         
        }

Sorting the data
Place after:
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "NameOfTable")

      
let sorter = NSSortDescriptor(key: "nameOfTheAttributeBeingSorted", ascending: true)
        fetchRequest.sortDescriptors = [sorter]

Writing data to table view
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate{
implement functions:
numberOfSections
cellForRowAt
numberOfRowsInSection

Your entity can be used as a class, to be stored in an array:
var tasks: [Tasks] = []
In the above case, task is an entity.

numberOfRowsSelection:
return tasks.count

Create a new function to fetch the data:
func getData()
    {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        do
        {
        try tasks = context.fetch(Task.fetchRequest())
     
        }catch{print(error.localizedDescription)}
    }

In the above, tasks is an array used to store the data

Load the data into the table when it refreshes:

override ViewWillAppear:

getData()

tableView.reloadData()

cellForRowAt:
let cell = UITableViewCell()
//tells you which row
let oneTask = tasks[indexPath.row]
 cell.textLabel?.text = oneTask.nameOfTask
//nameOfTask is the attribute

return cell

Swipe to delete
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        if editingStyle == .delete
        {
            let taskToDelete = tasks[indexPath.row]
            context.delete(taskToDelete)
            (UIApplication.shared.delegate as! AppDelegate).saveContext()
            //fetch data again and reload table
            do
            {
                try tasks = context.fetch(Task.fetchRequest())
            }catch{}
         
     
        }
        ViewMyTasks.reloadData()
    }