如何使用 NSFechedResultController 从 NSSet 中删除与核心数据中的一对多相关的对象？

Question

我的核心数据图必须是实体，即 APBook 实体与 APLippingExtract 有一对多的关系。一本书可以有很多剪报。
RootTableViewController，它在部分中显示作者姓名，在行中显示他们的书籍。在 DetailTableViewController 中，从 APClippingExtract 实体中获取数据如下 -

@implementation DetailTableViewController

#pragma mark - fetchedResultController
- (NSFetchedResultsController*) fetchedResultController {

if (_fetchedResultController != nil) {
    return _fetchedResultController;
}

NSFetchRequest *request = [[NSFetchRequest alloc]initWithEntityName:@"APClippingExtract"];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"extract" ascending:YES];
request.sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];

[request setPredicate:[NSPredicate predicateWithFormat:@"extractFromBook == %@", self.currentBook]];

request.fetchBatchSize = 20;
_fetchedResultController = [[NSFetchedResultsController alloc]initWithFetchRequest:request managedObjectContext:self.mainContext sectionNameKeyPath:nil cacheName:nil];

//dlegating for NSfetchedResultController
_fetchedResultController.delegate =self;

return _fetchedResultController;
}

当用户删除带有裁剪的行时，下面的方法用于从实体中删除它。

-(void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath{

if (editingStyle == UITableViewCellEditingStyleDelete) {
    NSManagedObjectContext *context = self.mainContext;
    APClippingExtract *clippingToDelete = [self.fetchedResultController objectAtIndexPath:indexPath];

    [context deleteObject:clippingToDelete];

    [eeCoreStack saveMainContext];

}
}

EECoreStack是Core Stack setUp的自定义类//保存方法如下

- (void)saveMainContext {
[self.mainContext performBlock:^{
    NSError *error = nil;
    [self.mainContext save:&error];
    if(error){
        NSLog(@"ERROR SAVING MAIN MOC %@: %@:", [error localizedDescription], [error userInfo]);
    }else {
        [self saveMasterContext];
    }
}];
}

- (void)saveMasterContext {

    [self.masterContext performBlock:^{
        NSError *error = nil;
        [self.masterContext save:&error];
        if(error){
            NSLog(@"ERROR SAVING MASTER CONTEXT %@; : %@", [error localizedDescription], [error userInfo]);
        }
    }];
}

问题是删除行时，返回 RootTableViewController 时，numberOfClipping 计数没有改变。

APBook类中有一个方法

- (void)removeSmallClippings:(NSSet<APClippingExtract *> *)values;

为了上面的工作，需要获取 APBook 属性。因为我目前正在 DetialTableViewController 中获取 APClippingExtract。

如有错误请指正。

编辑 1：

RootTableViewController

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{

if([segue.identifier isEqualToString:@"ListSegue"]){

    ListTableViewController *destination = (ListTableViewController *)segue.destinationViewController;

    NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
    APBook *selectedBook = (APBook*)[self.fetchedResultController objectAtIndexPath:indexPath];

    destination.currentBook = selectedBook;
    destination.mainContext = self.mainContext;
    destination.workerContext = self.workerContext;


    destination.deleteNow = ^(APClippingExtract *deleteClipping){
        [self.mainContext deleteObject:deleteClipping];
        deleteClipping.extractFromBook.numberOfClippings = deleteClipping.extractFromBook.numberOfClippings;
        [eeCoreStack saveMainContext];

    };
}
}

在 DetailTableViewController 中

-(void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath{
if (editingStyle == UITableViewCellEditingStyleDelete) {

    APClippingExtract *clippingToDelete = [self.fetchedResultController objectAtIndexPath:indexPath];
    self.deleteNow(clippingToDelete);


}

}

Answer 1

修改对象（包括删除）不会触发其相关对象的任何更新。这意味着正在监视相关对象的 FRC 不会触发。您要做的就是自己修改相关对象。确切地说，我不知道你有什么属性，但这里有一个例子。

clipping.book.title = clipping.book.title; // This will trigger FRCs watching book entities.

[context deleteObject:clipping];