swift - 如何对数组中的每个对象执行 fetchRequest 计数？

Question

我有 2 个实体:

出席:

import Foundation
import CoreData

extension Attendance {

    @NSManaged var date: NSDate?
    @NSManaged var id: NSNumber?
    @NSManaged var id_consultant: String?
    @NSManaged var id_store: NSNumber?
    @NSManaged var name: String?
    @NSManaged var status: String?

}

和产品:

import Foundation
import CoreData

extension Product {

    @NSManaged var id: String?
    @NSManaged var name: String?
    @NSManaged var preco: String?
    @NSManaged var attendance: Attendance?

}

我正在获取所有出勤，并且需要执行获取来计算出勤中有多少产品:

这是我获取考勤的方法。如何获取带有考勤 ID 的产品数量？

  func fetchAttendances() {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    let managedContext = appDelegate.managedObjectContext

    let fetchRequest = NSFetchRequest(entityName: "Attendance")
    let attendancePredicate = NSPredicate(format: "id_store == \(Int(Helper.userDefaults().objectForKey(ConstantHelper.kIdStore)! as! NSNumber))")
    fetchRequest.predicate = attendancePredicate

    do {
        let results = try managedContext.executeFetchRequest(fetchRequest)
        myAttendances = results as! [NSManagedObject]



        self.collectionAttendances.reloadData()
    } catch let error as NSError {
        print("Could not fetch \(error), \(error.userInfo)")
    }
}

Answer 1

假设您已设置数据模型，以便考勤和产品具有一对多关系...

Attendance <---->> Product

...您可以利用 map 语法以非常简洁的方式完成此操作:

let countArray = attendanceArray.map { ($0.id, $.products?.count ?? 0) }

这将返回一个包含 id 和产品数量的元组数组。