在 IOS 中获取 CoreData

Question

我是 CoreData 的新手，我正在学习一些教程。

这是我的数据模型：

我想构建类似于实时乐谱的东西。所以我添加了一些遵循这种格式的演示数据：

// -------------------------------------------------------------------------
// --   GW :    1                                           2
//              |                                           |
//          Premier League                               Primera
//         /            \                                   |
//  Chelsea vs M.City  Arsenal vs Liverpool      Real Mad vs Barcelona
// -------------------------------------------------------------------------

我可以验证它们是否已保存，正如您从下面的屏幕截图中看到的那样：

所以，现在我需要做的就是将这些数据提取到我的应用程序中。我已经添加了这些调试功能：

# pragma -
# pragma  mark - different fetch functions

- (void) fetchGameweeksAndLeagues {
    /*
     Set up the fetched results controller.
     */
    NSLog(@"Fetch Gameweeks and Leagues");
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entityGW = [NSEntityDescription entityForName:@"GameWeek" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entityGW];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    NSError *fetchError = nil;
    NSArray *result = [self.managedObjectContext executeFetchRequest:fetchRequest error:&fetchError];

    if (!fetchError) {
        for (NSManagedObject *managedObject in result) {
            NSLog(@"GwId:%@, League: %@", [managedObject valueForKey:@"gwId"], [[managedObject valueForKey:@"leagues"] valueForKey:@"leagueName"]/*,[[managedObject valueForKey:@"matches"] valueForKey:@"homeTeam"],[[managedObject valueForKey:@"matches"] valueForKey:@"awayTeam"]*/);
        }

    } else {
        NSLog(@"Error fetching data.");
        NSLog(@"%@, %@", fetchError, fetchError.localizedDescription);
    }
}

-(void) fetchMatchesForLeagueWithId/*:(NSNumber*)leagueId*/
{
    NSLog(@"Fetch Matches for specific League");
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entityLeague = [NSEntityDescription entityForName:@"League" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entityLeague];


    NSError *fetchError = nil;
    NSArray *result = [self.managedObjectContext executeFetchRequest:fetchRequest error:&fetchError];

    if (!fetchError) {
        for (NSManagedObject *managedObject in result) {
            NSLog(@"League: %@, Teams : %@ vs %@", [managedObject valueForKey:@"leagueName"],[[managedObject valueForKey:@"matches"] valueForKey:@"homeTeam"],[[managedObject valueForKey:@"matches"] valueForKey:@"awayTeam"]);
        }
    } else {
        NSLog(@"Error fetching data.");
        NSLog(@"%@, %@", fetchError, fetchError.localizedDescription);
    }
}

所以，我的输出是：

2015-03-24 17:38:42.236 SofaRef[73743:2215371] GwId:1, League: {(
    "Premier League"
)}
2015-03-24 17:38:42.236 SofaRef[73743:2215371] GwId:2, League: {(
    Primera
)}
2015-03-24 17:38:42.236 SofaRef[73743:2215371] Fetch Matches for specific League
2015-03-24 17:38:42.237 SofaRef[73743:2215371] League: Primera, Teams : {(
    "Real Madrid"
)} vs {(
    Barcelona
)}
2015-03-24 17:38:42.237 SofaRef[73743:2215371] League: Premier League, Teams : {(
    Chelsea,
    Arsenal
)} vs {(
    Liverpool,
    "Man.City"
)}

那么，我怎样才能以正确的顺序打印它们？

我想以与它们在数据库中相同的方式并以相同的顺序实际打印它们。这意味着打印切尔西 vs 曼城和阿森纳 vs 利物浦，而不是“按”列“分组” - 我想将它们作为“行”获取。

Answer 1

因为 League 与 Match 的关系是一对多的，所以 League 的 matches 属性返回一个 NSSet，即 [managedObject valueForKey:@"matches"] 是一个 NSSet。在您的 NSLog 语句中，您使用：

[[managedObject valueForKey:@"matches"] valueForKey:@"homeTeam"]

这会获取上述 NSSet 的每个元素，获取 homeTeam 属性值，并将结果作为新的 NSSet 返回。当你记录这个 NSSet 时，它会列出所有的值：

{(
    Chelsea,
    Arsenal
)}

但是由于 NSSet 是无序的，结果可能是任何顺序的。事实上，正如您的结果所示，价值

[[managedObject valueForKey:@"matches"] valueForKey:@"awayTeam"]

是相反的顺序：

{(
    Liverpool,
    "Man.City"
)}

您需要做的是分别记录每个match，显示每个homeTeam 和awayTeam。您可以通过嵌套另一个 for 循环来做到这一点：

    for (NSManagedObject *managedObject in result) {
        NSLog(@"League: %@", [managedObject valueForKey:@"leagueName"]);
        for (NSManagedObject *match in [managedObject valueForKey:@"matches"]) {
            NSLog(@"Teams : %@ vs %@", [match valueForKey:@"homeTeam"],[match valueForKey:@"awayTeam"]);
        }
    }

这将确保您的输出出现在“行”而不是“列”中。但它仍然以随机序列呈现匹配，这可能与 SQL 数据库中的序列匹配也可能不匹配。通常，您不应假定数据库中的条目是按任何特定顺序排列的。如果顺序很重要，则应在从数据库中获取值时指定它（或在获取它们后对其进行排序）。为此，请使用NSSortDescriptor。假设您的偏好是匹配按字母顺序使用homeTeam 排序；使用以下 sortDescriptor：

NSSortDescriptor *homeTeamSort = [NSSortDescriptor sortDescriptorWithKey:@"homeTeam" ascending:YES];

你要排序的集合是matches关系，所以修改上面的代码如下：

    for (NSManagedObject *managedObject in result) {
        NSLog(@"League: %@", [managedObject valueForKey:@"leagueName"]);
        NSSortDescriptor *homeTeamSort = [NSSortDescriptor sortDescriptorWithKey:@"homeTeam" ascending:YES];
        NSArray *sortedMatches = [[managedObject valueForKey:@"matches"] sortedArrayUsingDescriptors:@[homeTeamSort]];
        for (NSManagedObject *match in sortedMatches) {
            NSLog(@"Teams : %@ vs %@", [match valueForKey:@"homeTeam"],[match valueForKey:@"awayTeam"]);
        }
    }

Answer 2

//核心数据演示

import UIKit
import CoreData

class ViewController: UIViewController

{
@IBOutlet var txt_add: UITextField!
@IBOutlet var txt_name: UITextField!
let contex = ((UIApplication.shared.delegate) as! AppDelegate).persistentContainer.viewContext;
override func viewDidLoad()
{
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}
@IBAction func btn_insert(_ sender: UIButton)
{
    let entity = NSEntityDescription.insertNewObject(forEntityName: "Employee", into: contex);
    entity.setValue(txt_name.text, forKey: "empname");
    entity.setValue(txt_add.text, forKey: "empadd");
    do
    {
        try contex.save();
    }
    catch
    {

    }
}
@IBAction func btn_select(_ sender: UIButton)
{
    let entitydic = NSEntityDescription.entity(forEntityName: "Employee", in: contex);
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Employee")
    request.entity = entitydic;
    let pred = NSPredicate(format: "(empname = @%)", txt_name.text!);
    request.predicate = pred;
    do
    {
        let arr = try contex.fetch(request);
        if arr.count > 0
        {
            let obj = arr[0] as! NSManagedObject;
            txt_name.text = obj.value(forKey: "empname") as? String;
            txt_add.text = obj.value(forKey: "empadd") as? String;
        }
    }
    catch
    {

    }
}
@IBAction func btn_update(_ sender: UIButton)
{
    let entitydic = NSEntityDescription.entity(forEntityName: "Employee", in: contex);
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Employee")
    request.entity = entitydic;
    let pred = NSPredicate(format: "(empname = %@)", txt_name.text!);
    request.predicate = pred;

    do
    {
        let arr = try contex.fetch(request);
        if arr.count > 0
        {
            let obj = arr[0] as! NSManagedObject;
            obj.setValue(txt_name.text, forKey: "empname");
            obj.setValue(txt_add.text, forKey: "empadd");

            do
            {
                try  contex.save();
            }
            catch
            {

            }
        }
    }
    catch
    {

    }

}

@IBAction func btn_delete(_ sender: UIButton)
{
    let entitydic = NSEntityDescription.entity(forEntityName: "Employee", in: contex);
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Employee");
    request.entity = entitydic;
    let pred = NSPredicate(format:"(empname = %@)", txt_name.text!);
    request.predicate = pred;
    do
    {
        let arr = try contex.fetch(request);
        if arr.count > 0
        {
            let obj = arr[0] as! NSManagedObject;
            contex.delete(obj)

            do
            {
                try contex.save();
            }
            catch
            {

            }
        }
    }
    catch
    {

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