How to set default value in core data array ? How to override the default value ? How to customize c-CodePudding

I'm trying to make a Storage Expiration Notification APP.

I create a class called Product, here are the properties.

@NSManaged public var productName: String?
@NSManaged public var quantity: String?
@NSManaged public var category = ["", "Food", "Daily", "Makeup"]
@NSManaged public var chooseCategory: Int16
@NSManaged public var purchaseDate: String?
@NSManaged public var expiredDate: String?
@NSManaged public var productID: String?

But there's an Error showed that @NSManaged property cannot have an initial value

Hence, I only can move the Category array(use picker controller to choose the values) to ViewContorller.swift. But I want to create a Customize Category array that users can change the value. For instance, the default category is ["Food", "Daily", "Makeup"], users can change the value to ["Drink", "Wine", "Battery"]. Should I use archiving, or create a new class? I have no idea how to implement it.

CodePudding user response：

The Core Data way to do this is by overriding awakeFromInsert. That function is inherited from NSManagedObject and is called once when the object is first inserted into a managed object context. For this case it would look something like

func awakeFromInsert() {
    category = ["", "Food", "Daily", "Makeup"]
}

It doesn't work in exactly the same way as a Swift initial value but it has the same effect since it happens when you create a new instance.

CodePudding user response：

A @NSManaged property cannot even be an array.

A lightweight Swift solution is a JSON string attribute and a computed property for the conversion.

@NSManaged public var category : String

and

var categoryArray : [String] {
    get { (try? JSONDecoder().decode([String].self, from: Data(category.utf8))) ?? [] }
    set {
        let data = try! JSONEncoder().encode(newValue)
        category = String(data: data, encoding: .utf8)!
    }
}

Set the default value

"[\"\",\"Food\",\"Daily\",\"Makeup\"]

either in awakeFromInsert or in Interface Builder in the model