Swift - 为相关的 CoreData 实体赋值

Question

我正在构建一个具有两个 CoreData 实体的应用 - 锻炼和锻炼。两者的关系是多对多的。

该应用程序是一对基本的 tableViewControllers，允许您将锻炼 (workoutName) 添加到 Workouts 实体，然后在下一个 tableViewController 中将锻炼添加到该 Workout。我正在努力解决的是如何将每个练习分配回它源自 CoreData 的锻炼。本质上，我要做的是在向练习实体添加 newExercise（使用练习名称变量）时在锻炼实体中设置锻炼名称值。

我通过来自 Workouts tableViewController 的 segue 将锻炼名称作为 var 锻炼传递给锻炼 tableViewController。

我也有多对多关系，并在 NSManagedObjects 文件中设置为 NSSet，但不知道如何使用它们。

这是练习设置的 tableViewController：

import UIKit
import CoreData

class ExerciseMasterTableViewController: UITableViewController {

// Declare workout variable
var workout: Workouts!

// Create an empty array of Exercises
var exercises = [Exercises]()

// Retreive the managedObjectContext from AppDelegate
let managedObjectContext = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext

override func viewDidLoad() {
    super.viewDidLoad()

    // Use optional binding to confirm the managedObjectContext
    if let moc = self.managedObjectContext {
    }

    fetchExercises()
}

func fetchExercises() {
    let fetchRequest = NSFetchRequest(entityName: "Exercises")

    // Create a sort descriptor object that sorts on the "exerciseName"
    // property of the Core Data object
    let sortDescriptor = NSSortDescriptor(key: "exerciseName", ascending: true)

    // Set the list of sort descriptors in the fetch request,
    // so it includes the sort descriptor
    fetchRequest.sortDescriptors = [sortDescriptor]

    if let fetchResults = managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [Exercises] {
        exercises = fetchResults
    }
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // How many rows are there in this section?
    // There's only 1 section, and it has a number of rows
    // equal to the number of exercises, so return the count
    return exercises.count
}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = self.tableView.dequeueReusableCellWithIdentifier("Exercise Cell", forIndexPath: indexPath) as UITableViewCell

    // Get the Exercises for this index
    let exercise = exercises[indexPath.row]

    // Set the title of the cell to be the title of the exercise
    cell.textLabel!.text = exercise.exerciseName
    cell.detailTextLabel!.text = "\(exercise.sets)x\(exercise.reps)"
    cell.accessoryType = UITableViewCellAccessoryType.DisclosureIndicator
    return cell
}

override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
    if(editingStyle == .Delete ) {
        // Find the Exercise object the user is trying to delete
        let exerciseToDelete = exercises[indexPath.row]

        // Delete it from the managedObjectContext
        managedObjectContext?.deleteObject(exerciseToDelete)

        // Refresh the table view to indicate that it's deleted
        self.fetchExercises()

        // Tell the table view to animate out that row
        tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
        save()
    }
}

// MARK: UITableViewDelegate
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    let exercise = exercises[indexPath.row]
}

let addExerciseAlertViewTag = 0
let addExerciseTextAlertViewTag = 1


@IBAction func addExerciseButton(sender: AnyObject) {
    var namePrompt = UIAlertController(title: "Add Exercise",
        message: "Enter Exercise Name",
        preferredStyle: .Alert)

    var exerciseNameTextField: UITextField?
    namePrompt.addTextFieldWithConfigurationHandler {
        (textField) -> Void in
        exerciseNameTextField = textField
        textField.placeholder = "Exercise Name"
    }

    namePrompt.addAction(UIAlertAction(title: "Ok",
        style: .Default,
        handler: { (action) -> Void in
            if let textField = exerciseNameTextField {
                self.saveNewItem(textField.text, workoutName: workouts.workoutName)
            }
    }))

    self.presentViewController(namePrompt, animated: true, completion: nil)
}

func saveNewItem(exerciseName : String, workoutName: String) {

    // Create the new exercise item
    var newExercise = Exercises.createExerciseInManagedObjectContext(self.managedObjectContext!, exerciseName: exerciseName, workoutName: workoutName)

    // Update the array containing the table view row data
    self.fetchExercises()

    // Animate in the new row
    // Use Swift's find() function to figure out the index of the newExercise
    // after it's been added and sorted in our Exercises array
    if let newExerciseIndex = find(exercises, newExercise) {
        // Create an NSIndexPath from the newExerciseIndex
        let newExerciseIndexPath = NSIndexPath(forRow: newExerciseIndex, inSection: 0)
        // Animate in the insertion of this row
        tableView.insertRowsAtIndexPaths([ newExerciseIndexPath ], withRowAnimation: .Automatic)
        save()
    }

}

func save() {
    var error : NSError?
    if(managedObjectContext!.save(&error) ) {
        println(error?.localizedDescription)
    }
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
    if segue.identifier == "exerciseSettings" {
        let ExerciseSettingsDetailViewController = segue.destinationViewController as UIViewController
        let indexPath = tableView.indexPathForSelectedRow()!
        let exercise = exercises[indexPath.row]
        let destinationTitle = exercise.exerciseName
        ExerciseSettingsDetailViewController.title = destinationTitle
    }
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

另外，这里是在我的练习类中定义的函数 createExerciseInManagedObjectContext 添加一个新的练习：

    class func createExerciseInManagedObjectContext(moc: NSManagedObjectContext, exerciseName: String, workoutName: String) -> Exercises {
    let newExercise = NSEntityDescription.insertNewObjectForEntityForName("Exercises", inManagedObjectContext: moc) as Exercises

    newExercise.exerciseName = exerciseName
    self.workouts.addObject(workoutName)

    return newExercise
}

我可以将所选锻炼 (workoutName) 的字符串传递给此函数，但不知道如何通过锻炼与锻炼实体的关系来设置它。

这是我的练习实体：

import Foundation
import CoreData

class Exercises: NSManagedObject {

@NSManaged var exerciseName: String
@NSManaged var sets: NSNumber
@NSManaged var reps: NSNumber
@NSManaged var repWeight: NSNumber
@NSManaged var barWeight: NSNumber
@NSManaged var incrementWeight: NSNumber
@NSManaged var workouts: NSSet

class func createExerciseInManagedObjectContext(moc: NSManagedObjectContext, exerciseName: String, workoutName: String) -> Exercises {
    let newExercise = NSEntityDescription.insertNewObjectForEntityForName("Exercises", inManagedObjectContext: moc) as Exercises

    newExercise.exerciseName = exerciseName
    newExercise.workouts.setByAddingObject(workoutName)

    return newExercise
}

}

这是我的锻炼实体：

import Foundation
import CoreData

class Workouts: NSManagedObject {

@NSManaged var workoutName: String
@NSManaged var sessions: NSSet
@NSManaged var exercises: NSSet

class func createWorkoutInManagedObjectContext(moc: NSManagedObjectContext, workoutName: String) -> Workouts {
    let newWorkout = NSEntityDescription.insertNewObjectForEntityForName("Workouts", inManagedObjectContext: moc) as Workouts
    newWorkout.workoutName = workoutName

    return newWorkout
}

}

Answer 1

如果您正确设置模型，两个实体将通过关系相互引用。您将实体添加到另一个实体，而不是它的名称（这是一个属性）。

Core Data 应该在您创建 NSManagedObject 子类时自动生成访问器。有了这些，在锻炼中添加新的（或现有的）锻炼非常简单：

workout.addExercisesObject(newExercise)

这假设你的关系被称为 exercises。

所以实际上最好将实际的锻炼对象传递给函数而不是它的名称。不要忘记保存。

编辑：
为了使它起作用，您有两个选择。

您可以让 Xcode 在 Objective-C 中生成 NSManagedObject 子类并自动配置桥接头。然后您无需任何努力即可获得访问器。

或者你必须自己实现它们。例如：

@objc(Exercise)
class Exercise: NSManagedObject {

@NSManaged var workouts: NSSet

    func addWorkoutsObject(value: Workout!) {
        var mutableWorkouts = self.workouts.mutableCopy() as! NSMutableSet
        mutableWorkouts.addObject(value)
        self.workouts = mutableWorkouts as NSSet
    }
} 

请注意，我没有添加键值编码调用，因此除非您添加它们，否则 KVO 将无法工作。