Read, update and delete

Question

Swift, Storyboards, Core Data

I have this code that makes an insert with Core Data. How would it be read, update and delete in this specific case?

I have seen a lot of tutorials and each one makes things a bit different. I could not adapt to this case.

(I have already created the data model with the entity Users and the Attrituves name and password. I also have linked the buttons read, update and delete. I am looking for the most bàsic, without tables... Just like the insert I have here. Thank you!)

import UIKit
import CoreData

class ViewController: UIViewController {

    @IBOutlet weak var name: UITextField!
    @IBOutlet weak var password: UITextField!
  
    lazy var context : NSManagedObjectContext = {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        return appDelegate.persistentContainer.viewContext
    }()

  
    // INSERT
    @IBAction func button(_ sender: UIButton) {
        guard name.hasText && password.hasText else {
            return
        }

        let user = Users(context: context)
        user.name = self.name.text!
        user.password = self.password.text!
        do {
            try context.save()
            print ("saved")
        } catch {
            print(error)
        }
      
    }

    // READ 
    @IBAction func readButton(_ sender: UIButton) {

    }
   
    // UPDATE
    @IBAction func updateButton(_ sender: UIButton) {

    }
   
    // DELETE 
    @IBAction func deleteButton(_ sender: UIButton) {
       
    }
}

Swift

1.6k

Posted by

narcisfromgirona

Reply

Add a Comment

Answer 1

they put the context outside the crud

No, they create the context in each func.

But no problem to put it out of each func:

class ViewController: UIViewController {

    var appDelegate: AppDelegate?
    var managedContext: NSManagedObjectContext?
 
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
     
       appDelegate = UIApplication.shared.delegate as? AppDelegate
       managedContext = appDelegate?.persistentContainer.viewContext
    }

Just take care when calling managedContext later to use managedContext?

For instance how to:

- Read: how to call the context (lazy var context) and then read all the pairs name - password that the database has.

I thought I wrote the way to do it for read.

What is not working ?

Posted by

Claude31

Add a Comment

Answer 2

As you don't show your CoreData structure, it is nopt possible to say exactly how to do.

But it should be easy if you follow this tutorial:

h ttps://medium.com/@ankurvekariya/core-data-crud-with-swift-4-2-for-beginners-40efe4e7d1cc

Posted by

Claude31

Add a Comment

Answer 3

The structure is, as I said in the question: the Entity Users and the attributes name (String) and password (String). That is all

Posted by

narcisfromgirona

Add a Comment

Answer 4

Yes, but you don't tell what the keys are…

But, you should have no problem, with such a simple structure, to implement what is described in tutorial.

For instance, to read, will be like (once again, you did not tell what the keys are, so just guess):

        func read() {
          
            // container is set up in the AppDelegates so we need to refer that container.
            guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
          
            // create a context from this container
            let managedContext = appDelegate.persistentContainer.viewContext
          
            // Prepare the request of type NSFetchRequest  for the entity
            let fetchRequest = NSFetchRequest(entityName: "Users")
          
            do {
                let result = try managedContext.fetch(fetchRequest)
                for data in result as! [NSManagedObject] {     // Do what you need with date, store in a table, …
                    print(data.value(forKey: "username") as! String)
                    print(data.value(forKey: "pawdKey") as! String)
              }
              
            } catch {
                print("Failed")
            }
        }

What is this button exactly ? Specific to a record ? If so, adapt the request as needed

    @IBAction func readButton(_ sender: UIButton) { 
           read()
    }

Note: calling an IBAction "button" may not be the most helful for future maintenance of your code.

Posted by

Claude31

Add a Comment

Answer 5

I think I understand the tutorial. That information is useful. Thank you. But I do not know how to apply that to the way to do things in the Insert that I show in the question. If I understand, in that case, they put the context outside the crud, they do not do that in each crud. Only once at the beginning.

For instance how to:

- Read: how to call the context (lazy var context) and then read all the pairs name - password that the database has.

- Update: how to call the context and then update the password for the name John (for instance)

- Delete: how to call the context and delete the name John and its password

Posted by

narcisfromgirona

Add a Comment

Answer 6

they put the context outside the crud

No, they create the context in each func.

But no problem to put it out of each func:

class ViewController: UIViewController {

    var appDelegate: AppDelegate?
    var managedContext: NSManagedObjectContext?
 
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
     
       appDelegate = UIApplication.shared.delegate as? AppDelegate
       managedContext = appDelegate?.persistentContainer.viewContext
    }

Just take care when calling managedContext later to use managedContext?

For instance how to:

- Read: how to call the context (lazy var context) and then read all the pairs name - password that the database has.

I thought I wrote the way to do it for read.

What is not working ?

Posted by

Claude31

Add a Comment

Answer 7

Yes, read works well. Thank you.

Now I am working on this.

Posted by

narcisfromgirona

Add a Comment

Read, update and delete

Accepted Reply

Replies