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--- swift [2023/10/25 20:45]
admin
+++ swift [2023/11/19 22:16] (current)
admin
@@ Line 76: / Line 76: @@
 [[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]]
+### Relationship: Connect entities in CoreData
+ref: https://www.hackingwithswift.com/books/ios-swiftui/one-to-many-relationships-with-core-data-swiftui-and-fetchrequest
+. Create Entities in CoreData
+. Select the relationship created, in the right tool panel, change `Type` to `To Many`
+. Select the entity, in the right tool panel, change `Codegen` to `Manual/None`
+. Use `Editor>Create NSManagedObject SubClass...` menu to create `...CoreDataClass` file and `...CoreDataProperties` file for each entity.
+. 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)
+}
+```
+. Edit ` ...CoreDataProperties` file, add code like `public var wrappedCapacity: NSDecimalNumber { capacity ?? 0.0 }`
+. 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
+       }
+   }
+```
+. 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
+                 }
+             }
+         }
+      }
+   }
+}
+```
+. 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()
+```
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