如何使用键（字符串）和结果（nsfetchrequestresult）定义pectractedfetchresults的扩展

Question

我的 plocteredfetchresults 按这样的定义：

private var consumption: SectionedFetchResults<String?, MedicationConsumption>

药物消费的数量可变。我需要写扩展，以进行消费，它将具有功能 totalQuantity 。我尝试过各种方法来扩展它，但没有任何运气。

如何在 phoctereDfetchResults上写扩展名，它将返回 totalQuantity ??

不起作用的第1个扩展：

extension SectionedFetchResults where Result == NSManagedObject {
    var totalQuantity: Int { /* Code here */ }
}

不编译的第二个扩展名

extension SectionedFetchResults<String, NSFetchRequestResult>.Element {
    var totalQuantity: Int { /* Code here */ }
}

：代码：

static var fetchRequest: NSFetchRequest<MedicationConsumption> {
    let result = MedicationConsumption.fetchRequest()
    result.sortDescriptors = [NSSortDescriptor(keyPath: \MedicationConsumption.date, ascending: true)]
    result.predicate = NSPredicate(format: "(medication.type == 1)")
    return result
}
@SectionedFetchRequest(fetchRequest: Self.fetchRequest, sectionIdentifier: \MedicationConsumption.group)
private var consumption: SectionedFetchResults<String?, MedicationConsumption>

// Use case scenario
var body: some View {
    List(waterConsumption) { section in
        VStack {
            Text("\(section.totalQuantity)")
        }
    }
}

药物消费：nsmanagedObject

extension MedicationConsumption {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<MedicationConsumption> {
        return NSFetchRequest<MedicationConsumption>(entityName: "MedicationConsumption")
    }

    @NSManaged public var date: Date?
    @NSManaged public var group: String?
    @NSManaged public var quantity: Double
    @NSManaged public var medication: Medication?
}

Answer 1

我认为这可能就像

1. 是总的响应：

extension SectionedFetchResults where Result == MedicationConsumption {
    var totalQuantity: Double {
        self.reduce(0) { sum, section in
            section.reduce(into: sum) { $0 += $1.quantity }
        }
    }
}

2. 对于总计

extension SectionedFetchResults.Section where Result == MedicationConsumption {
    var totalQuantity: Double {
        self.reduce(0) { $0 + $1.quantity }
    }
}

项目中的测试模块