Core Data

✢ query

//from Entity: Employee
let entity = NSEntityDescription.entity(forEntityName: "Employee", in: self.moc)
//sort by: entryDate
let sortDescriptor = NSSortDescriptor(key: "entryDate", ascending: true)
//when predicate: 2017/3 < entryDate < 2017/6
let predicate = NSPredicate(format: "entryDate > %lf AND entryDate < %lf", start, end)
//create request
let request = NSFetchRequest<NSFetchRequestResult>()
request.entity = entity
request.predicate = predicate
request.sortDescriptors = [sortDescriptor]
do {
    let results = try moc.executeFetchRequest(request) as! [Employee]
    for result in results {
        print("Employee ID: \(results.id)")
    }
} catch {
    fatalError("Failed to fetch data: \(error)")
}

✢ Concepts

  • Core data will not get real data when recevie request.
    • In order to improve performance, Core data would not return real data when recevie request. Than return real data when program needs those data to do some operations, for example: show data in screen.
    • If needed to return real data all the time. Add code:
      request.returnsObjectsAsFaults = true
      • true: real data all the time
      • false: real data when needed


✢ References

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