Fetch specific attributes from coredata swift

Question

I am developing core data in my application. I want to fetch name attribute from the core data.

class ViewController: UIViewController {

@IBOutlet weak var saveDataBtn:UIButton!
@IBOutlet weak var dataTxtField:UITextField!
@IBOutlet weak var dataLbl:UILabel!
var tasks: [Task] = []
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

@IBAction func saveDataBtnPressed(_sender : UIButton){
    print("Save Data.")
    let task = Task(context: context)
    task.name = dataTxtField.text
    (UIApplication.shared.delegate as! AppDelegate).saveContext()
    getData()
}

func getData(){
    do{
        tasks = try context.fetch(Task.fetchRequest())

    }catch{
        print("Fetching Failed")

    }

}

How can i get it?

Thanks,

Fetch the Task object you're interested in and read its "name" property. — Phillip Mills
– Phillip Mills, Commented Oct 13, 2017 at 15:17
I have already fetch task object. but i am not able to read name property — user12346
– user12346, Commented Oct 13, 2017 at 15:19
Can you please let me know that how can i get the name property from task object — user12346
– user12346, Commented Oct 13, 2017 at 15:21
What does "i am not able to read name property" mean? You use task.name to set it, do you get an error if you read it the same way? — Phillip Mills
– Phillip Mills, Commented Oct 13, 2017 at 15:29

mrfour · Accepted Answer · 2017-10-14 01:26:55Z

10

In Swift 4, you can access the property directly.

do {
    let tasks = try context.fetch(request)
    for task in tasks {
        print(task.name)
    }
} catch let error {
    print(error.localizedDescription)
}

UPDATED - How to delete and update an instance of an Entity.

Here are some ideas to organize the code to deal with the updating and deleting.

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

extension Task {
    // to get an instance with specific name
    class func instance(with name: String) -> Task? {
        let request = Task.fetchRequest()

        // create an NSPredicate to get the instance you want to make change
        let predicate = NSPredicate(format: "name = %@", name)
        request.predicate = predicate

        do {
            let tasks = try context.fetch(request)
            return tasks.first
        } catch let error {
            print(error.localizedDescription)
            return nil
        }
    }

    // to update an instance with specific name
    func updateName(with name: String) {
        self.name = name
        (UIApplication.shared.delegate as! AppDelegate).saveContext()
    }

    // to delete an instance
    func delete() {
        context.delete(self)
        (UIApplication.shared.delegate as! AppDelegate).saveContext()
    }
}

func howItWorks() {
   guard let task = Task.instance(with: "a task's name") else { return }
   task.updateName(with: "the new name")
   task.delete()
}

edited Oct 14, 2017 at 1:26

answered Oct 13, 2017 at 15:24

mrfour

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2 Comments

user12346 Over a year ago

Do you have an idea about to update and delete specific row in swift 4?

mrfour Over a year ago

I have updated the answer. But I still suggest reading this, developer.apple.com/library/content/documentation/Cocoa/….

Gurjinder Singh · Accepted Answer · 2020-02-01 16:52:14Z

In Swift 4.1 and 5. We will use NSPredicate to specify our required condition. NSFetchRequest has a property predicate will set our predicate here as follow.

    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext

    let fetch = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")
    let predicate = NSPredicate(format: "username = %@", argumentArray: ["John"]) // Specify your condition here
// Or for integer value
// let predicate = NSPredicate(format: "age > %d", argumentArray: [10])

    fetch.predicate = predicate

    do {

      let result = try context.fetch(fetch)      
      for data in result as! [NSManagedObject] {
        print(data.value(forKey: "username") as! String)
        print(data.value(forKey: "password") as! String)
        print(data.value(forKey: "age") as! String)
      }
    } catch {
      print("Failed")
    }

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