alexpaul/CoreData-Saving-Array.md

## CoreData-Saving-Array.md

      
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              CoreData-Saving-Array.md
            
          
    Core Data (Saving an array)

While saving an array to Core Data is supported, one of the first questions you will want to ask, if this array should be a relationship to another entity instead? It the answer is no, then continue reading on....
1. Core Data Model (Graphical Interface)

Set the attribute, in this case, the type you want to save as an array to Core Data supported type Binary Data
Example

attribute is hobbies
type would be Binary Data
2. Save the array to the entity instance

NSKeyedArchiver is a class that serializes (converts) data very similar to JSONEncoder
// saving an array [String] to a Core Data (Binary Data) type
// user is an instance of the User entity class
do {
  user.hobbies = try NSKeyedArchiver.archivedData(withRootObject: ["Fishing", "Biking", "Dancing"], requiringSecureCoding: true)
} catch {
  print("failed to archive array with error: \(error)")
}

Remember to save the NSManagedObjectContext.

3. Retrieve the array using the entity's attribute

NSKeyedUnArchiver is a class that de-serializes (re-converts) data back, very similar to JSONDecoder
NSArray.self - we have to specify what class we are getting back, the class needs to conform to the NSSecureCoding protocol and inherit from NSObject. In this case we are first
getting back an NSArray (Objective-C Array, keep in mind Core Data is an Objective-C API. After retrieving
the NSArray we use typecasting to convert it to a String array which we stored originally.)
if let hobbies = user.hobbies {
  do {
    if let hobbiesArr = try NSKeyedUnarchiver.unarchivedObject(ofClass: NSArray.self, from: hobbies) as? [String] {
      dump(hobbiesArr)
    }
  } catch {
    print("could not unarchive array: \(error)")
  }
}