核心数据按两个描述符排序数据

Question

我在ios应用中使用了核心数据。现在我有一个表，其中有两列。

1. 分类

2. 订单（其中有NSNumber 1,2,5）

我想获取数据，因此它将首先按类别名称而不是按订单号按字母顺序排序。

我使用了以下代码：

NSEntityDescription *entity_Maintness = [NSEntityDescription
                                             entityForName:@"Maintness" inManagedObjectContext:__managedObjectContext];
    [fetchRequest_Maintness setEntity:entity_Maintness];


    NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"type" ascending:YES];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"serialNumber" ascending:NO];


    NSArray *sortDescriptors12 = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor, nil];
    [fetchRequest_Maintness setSortDescriptors:sortDescriptors12];

但数据仅按类别而不是按序列号排序。

感谢您的帮助。

Answer 1

上面的代码看起来不错。也许你的代码中有其他问题？以下是我为您快速生成的一些代码，可以作为起点？

#import "MainViewController.h"
#import "Maintness.h"

@interface MainViewController ()
@property (weak, nonatomic) IBOutlet UITextField *type;
@property (weak, nonatomic) IBOutlet UITextField *serialNumber;
@property (strong, nonatomic) NSManagedObjectContext *context;
- (IBAction)addButtonPressed:(id)sender;
- (IBAction)retrieveButtonPressed:(id)sender;

@end

@implementation MainViewController

#pragma mark - lazy instantiation
- (NSManagedObjectContext *)context{
    if (!_context){
        id appDelegate = (id)[[UIApplication sharedApplication] delegate];
        _context = [appDelegate managedObjectContext];
    }
    return _context;
}

#pragma mark - core data interactions
- (IBAction)addButtonPressed:(id)sender {
    NSError *error = nil;

    Maintness *newMaintness = nil;

    newMaintness = [NSEntityDescription insertNewObjectForEntityForName:@"Maintness" inManagedObjectContext:self.context];

    newMaintness.type = self.type.text;
    newMaintness.serialNumber = self.serialNumber.text;

    if (![self.context save:&error]) {
        NSLog(@"Oh no - error: %@", [error localizedDescription]);
    } else {
        NSLog(@"It appears the details were added ok");
    }

}

- (IBAction)retrieveButtonPressed:(id)sender {
    NSError *error = nil;
    // Set up fetch
    NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
    // Set up entity
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Maintness" inManagedObjectContext:self.context];
    [fetch setEntity:entity];
    // Set up sorting
    //   - sorts in order of array
    NSSortDescriptor *primarySortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"type" ascending:YES];
    NSSortDescriptor *secondarySortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"serialNumber" ascending:NO];
    NSArray *sortDescriptors = @[primarySortDescriptor, secondarySortDescriptor];
    [fetch setSortDescriptors:sortDescriptors];

    NSArray *results = [self.context executeFetchRequest:fetch error:&error];

    for (Maintness *result in results) {
        NSLog(@"type: %@ serial number: %@", result.type, result.serialNumber);
    }
}
@end