尝试从核心数据中的两个实体中删除数据

Question

我尝试从两个实体中删除记录。核心数据有两个实体，名称 Student 和 Detail 都具有相反的关系。关系是

Student -> Detail:detail Detail -> Student:student

尝试从 table 视图中删除两个实体的记录。但是当我尝试删除时，只有实体 Student 从 delete 但从 detail Entity 无法删除。它向我显示了这个错误。

-[NSSet isSubsetOfSet:]: set argument is not an NSSet'

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source

        AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
        _mainContext = [appDelegate manageObjectContext];

        [_mainContext deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]];
        Detail *detailEntity = [self.fetchedResultsController objectAtIndexPath:indexPath];
        Student *studentEntity = [self.fetchedResultsController objectAtIndexPath:indexPath];

        NSMutableSet *mySet = [[NSMutableSet alloc] init];
        [mySet removeObject: detailEntity];
        [studentEntity removeDetail:mySet];
        studentEntity.detail = detailEntity;

        NSError *error = nil;
        if (![_mainContext save:&error]) {
            NSLog(@"Unresolve Error %@, %@", error, [error userInfo]);
            abort();
        }

        [self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];

    } 
}

StudentCoredataclass.h

#import "Student+CoreDataClass.h"


NS_ASSUME_NONNULL_BEGIN

@interface Student (CoreDataProperties)

+ (NSFetchRequest<Student *> *)fetchRequest;

@property (nullable, nonatomic, copy) NSString *name;
@property (nullable, nonatomic, copy) NSString *study;
@property (nullable, nonatomic, copy) NSString *number;
@property (nullable, nonatomic, retain) NSSet<Detail *> *detail;

@end

@interface Student (CoreDataGeneratedAccessors)

- (void)addDetailObject:(Detail *)value;
- (void)removeDetailObject:(Detail *)value;
- (void)addDetail:(NSSet<Detail *> *)values;
- (void)removeDetail:(NSSet<Detail *> *)values;

@end
NS_ASSUME_NONNULL_END

DetailCoredataclass.h

#import "Detail+CoreDataClass.h"


NS_ASSUME_NONNULL_BEGIN

@interface Detail (CoreDataProperties)

+ (NSFetchRequest<Detail *> *)fetchRequest;

@property (nullable, nonatomic, copy) NSString *address;
@property (nullable, nonatomic, copy) NSString *contact;
@property (nullable, nonatomic, copy) NSString *email;
@property (nullable, nonatomic, copy) NSString *number;
@property (nullable, nonatomic, retain) Student *student;

@end

FetchedResultController:

AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    _mainContext = [appDelegate manageObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Student"];

    // Add Sort Descriptors
    [fetchRequest setSortDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:NO]]];

    //[fetchRequest setRelationshipKeyPathsForPrefetching: @"detail"];
    // Initialize Fetched Results Controller
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_mainContext sectionNameKeyPath:nil cacheName:nil];

    // Configure Fetched Results Controller
    [self.fetchedResultsController setDelegate:self];

    // Perform Fetch
    NSError *error = nil;
    [self.fetchedResultsController performFetch:&error];

Answer 1

将您的代码替换为：

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
        NSManagedObjectContext *context = [appDelegate manageObjectContext];
        Student *studentEntity = [self.fetchedResultsController objectAtIndexPath:indexPath];
        [context deleteObject:studentEntity];
         NSError *error = nil;
        [context save:&error];
    } 
}

下一步在模型中设置Delete Rule删除学生时删除细节（反之亦然）。我不清楚为什么您将数据分成两个实体。

您不应在此处删除 tableView 的 Cell。当您从 fetchedResultsController 获得委托回调时，您应该将其删除。如果您还没有实施这些方法，那么您现在就实施吧。

Answer 2

请替换

[studentEntity removeDetail:mySet];

和

[studentEntity removeDetailObject:detailEntity];

尝试从核心数据中的两个实体中删除数据

Try to delete data from two entities in core data

entity

core-data

objective-c

delete-row

ios