CODEWITHSUNDEEP
iosswiftcore-dataswift2
Rajan Maheshwari
Rajan Maheshwari

Reputation: 14571

Cast from [Entity] to unrelated type Entity always fails in CoreData

I am using Swift 2.0 Xcode 7.0 and using Core Data in my app. I am facing trouble in fetching the results back from coredata. My entity name is User which is a subclass of NSManagedObject. When I created the NSManagedObject Subclass from editor, XCode 7 created two classes for me

  1. User.swift
  2. Extension class User+CoreDataProperties.swift

My User.swift class

import Foundation
import CoreData

class User: NSManagedObject {

// Insert code here to add functionality to your managed object subclass

}

User+CoreDataProperties.swift class import Foundation import CoreData

extension User {
@NSManaged var facebookId: String?
@NSManaged var googleId: String?
@NSManaged var userAge: NSNumber?
@NSManaged var userEmail: String?
@NSManaged var userId: NSNumber?
}

Now I managed to successfully save a record. Now when I am fetching it back I am using the following code. I am fetching a single record based on UserID

let fetchRequest = NSFetchRequest(entityName: "User")
fetchRequest.predicate = NSPredicate(format: "userId == %d",userId )

do {
     let fetchResults = try
     self.managedObjectContext.executeFetchRequest(fetchRequest) as? [User]

     // At this line I am getting warning 
     // Cast from [User] to unrelated type User always fails
     var userObj = fetchResults as! User

enter image description here

//How to get rid of the warning

//So how to fetch back and make changes in the object. I want to updates the change. For ex I want to do something like
     userObj.userAge = 30 //and then update this and save the context

    } 
     catch let fetchError as NSError {
    print("error: \(fetchError.localizedDescription)")
   }
    // if I use this line
    let user = fetchResults as [User]?
    // It does cast but then I am unable to find any of the members like userId, userAge in it. It says value of type [User]? has no member userAge

enter image description here

I saw this link and followed. But here no updation is done

http://www.sthoughts.com/2015/06/09/swift-2-0-snippet-coredata-fetching-with-error-handling/

Please help me in sorting this out. Any help will be appreciated.

Upvotes: 0

Views: 4291

Answers (2)

Martin R
Martin R

Reputation: 540005

The fetch request returns an array of objects (which can have zero, one, or more elements), even if you expect only a single result. In your case, you would simply access the first element of the result array:

let fetchResults = try
 self.managedObjectContext.executeFetchRequest(fetchRequest) as! [User]
if fetchResults.count > 0 {
    let user = fetchResults[0] //  `User`
    user.age = 24
    // ...
} else {
    // no matching user found ...
}

Alternatively:

if let user = fetchResults.first {
    user.age = 24
    // ...
} else {
    // no matching user found ...
}

Also note that you know that the fetched objects have the type User (because you configured the entities class in the Core Data model inspector), therefore a forced cast as! [User] is appropriate here.

Upvotes: 3

Michael
Michael

Reputation: 6515

The problem is that you mix User and [User]. The first one is a user-object, and it has a userAge property. The second one is a list of users and it doesn't have a userAge property. E.g. if a list users has two elements, then users[0] and users[1] were users, but users itself is just a list of users

Upvotes: 1

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