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swift [2023/10/25 20:45] – adminswift [2023/11/19 22:16] (current) – admin
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 [[https://developer.apple.com/library/archive/documentation/General/Conceptual/iCloudDesignGuide/Chapters/Introduction.html#//apple_ref/doc/uid/TP40012094|Apple: iCloud Design Guide]] [[https://developer.apple.com/library/archive/documentation/General/Conceptual/iCloudDesignGuide/Chapters/Introduction.html#//apple_ref/doc/uid/TP40012094|Apple: iCloud Design Guide]]
 [[https://developer.apple.com/library/archive/documentation/General/Conceptual/iCloudDesignGuide/Chapters/DesigningForKey-ValueDataIniCloud.html#//apple_ref/doc/uid/TP40012094-CH7|Apple: Designing for Key-Value Data in iCloud]] [[https://developer.apple.com/library/archive/documentation/General/Conceptual/iCloudDesignGuide/Chapters/DesigningForKey-ValueDataIniCloud.html#//apple_ref/doc/uid/TP40012094-CH7|Apple: Designing for Key-Value Data in iCloud]]
 +
 +### Relationship: Connect entities in CoreData
 +ref: https://www.hackingwithswift.com/books/ios-swiftui/one-to-many-relationships-with-core-data-swiftui-and-fetchrequest
 +
 +1. Create Entities in CoreData
 +2. Select the relationship created, in the right tool panel, change `Type` to `To Many`
 +3. Select the entity, in the right tool panel, change `Codegen` to `Manual/None`
 +4. Use `Editor>Create NSManagedObject SubClass...` menu to create `...CoreDataClass` file and `...CoreDataProperties` file for each entity.
 +5. In `...CoreDataProperties` file, you should be able to see code like below for adding transactions to this certain piggy object.
 +
 +```
 +extension Piggy {
 +
 +   @nonobjc public class func fetchRequest() -> NSFetchRequest<Piggy> {
 +       return NSFetchRequest<Piggy>(entityName: "Piggy")
 +   }
 +
 +   @NSManaged public var capacity: NSDecimalNumber?
 +   @NSManaged public var currentMoney: NSDecimalNumber?
 +   @NSManaged public var dailyAllowance: NSDecimalNumber?
 +   @NSManaged public var id: UUID?
 +   @NSManaged public var lastDepositDay: Date?
 +   @NSManaged public var name: String?
 +   @NSManaged public var totalSaved: NSDecimalNumber?
 +   @NSManaged public var transactions: NSSet?
 +}
 +extension Piggy {
 +  @objc(addTransactionsObject:)
 +  @NSManaged public func addToTransactions(_ value: PurchasedItem)
 +
 +  @objc(removeTransactionsObject:)
 +  @NSManaged public func removeFromTransactions(_ value: PurchasedItem)
 +
 +  @objc(addTransactions:)
 +  @NSManaged public func addToTransactions(_ values: NSSet)
 +
 +  @objc(removeTransactions:)
 +  @NSManaged public func removeFromTransactions(_ values: NSSet)
 +}
 +```
 +
 +1. Edit ` ...CoreDataProperties` file, add code like `public var wrappedCapacity: NSDecimalNumber { capacity ?? 0.0 }`
 +2. In  ` ...CoreDataProperties` file, `transactions` is an `NSSet`, perform the following steps to convert it from an `NSSet` to a `Set<PurchasedItem>` – a Swift-native type where the types of its contents is specificy to `PurchasedItem` type. Convert that `Set<PurchasedItem>` into an array, so that `ForEach` can read individual values from there. Sort that array, so the transactions come in a sensible order.
 +
 +```
 +   public var transactionArray: [PurchasedItem] {
 +       let set = transactions as? Set<PurchasedItem> ?? []
 +       
 +       return set.sorted {
 +           $0.wrappedTimestamp < $1.wrappedTimestamp
 +       }
 +   }
 +```
 +
 +1. Use them in your View: To read purchased items connected to a certain piggy in a View. Use the following code:
 +
 +```
 +   struct HistoryView: View {
 +       @Environment(\.managedObjectContext) private var viewContext
 +       @EnvironmentObject private var persistenceController: PersistenceController
 +       let piggy: Piggy
 +   
 +       @FetchRequest private var items: FetchedResults<PurchasedItem>
 +   
 +       init(piggy: Piggy) {
 +           _items = FetchRequest<PurchasedItem>(
 +               sortDescriptors: [NSSortDescriptor(keyPath: \PurchasedItem.timestamp, ascending: false)],
 +               predicate: NSPredicate(format: "piggyStored == %@", piggy)
 +           )
 +           self.piggy = piggy
 +       }
 +       
 +       var body: some View {
 +         NavigationView {
 +             if (items.count != 0) {
 +                 List {
 +                     ForEach(items) { item in
 +                       // view related code
 +                     }
 +                 }
 +             }
 +          }
 +       }
 +   }
 +```
 +
 +Or use the following code. However with this method the HistoryView won't update if you add new purchasedItem (transaction) because it is only monitoring the object `piggy`. To trigger view update when purchasedItem is added, you need to use the method above to fetch `PurchasedItem` directly.
 +
 +```
 +struct HistoryView: View {
 +   @Environment(\.managedObjectContext) private var viewContext
 +   @EnvironmentObject private var persistenceController: PersistenceController
 +   let piggy: Piggy
 +
 +   var body: some View {
 +     NavigationView {
 +         if (piggy.transactionArrary.count != 0) {
 +             List {
 +                 ForEach(piggy.transactionArray) { item in
 +                   // view related code
 +                 }
 +             }
 +         }
 +      }
 +   }
 +}
 +```
 +
 +1. To write new purchased item and connect it to piggy.
 +
 +```swiftUI
 + let newPurchase = PurchasedItem(context: viewContext)
 +   newPurchase.id = UUID()
 +   newPurchase.type = 0  // 0: purchase
 +   newPurchase.name = name
 +   newPurchase.price = NSDecimalNumber(decimal: Decimal(price))
 +   newPurchase.timestamp = Date()
 +   newPurchase.piggyStored = piggy
 +   try? viewContext.save()
 +```
 +
 +
  
 ## Icons ## Icons
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