[英]CoreData :NSFetchedResultsController one to many to many to many relationship
我在app上工作的是我使用核心數據,核心數據對象如下所示:
提供theaterName和genreName我想顯示actorsName。 有人知道建立
NSPredicate
的方法嗎?
您可以使用SUBQUERY來構建深入到“to many”關系的NSPredicates:
// Set predicate
NSPredicate *requestPredicate = [NSPredicate predicateWithFormat:@"SUBQUERY(genres, $g, ANY $g.movies.name == %@).@count != 0", @"Batman vs Superman"];
[fetchRequest setPredicate:requestPredicate];
UPDATE
根據您更新的示例,您將需要嵌套的子查詢,如下所示:
NSPredicate *requestPredicate = [NSPredicate predicateWithFormat:@"SUBQUERY(movies, $m, ANY $m.genres.name == %@).@count != 0 AND SUBQUERY(movies, $m, SUBQUERY($m.genres, $g, ANY $g.theaters.name == %@).@count != 0).@count != 0", @"Action", @"Harkins"];
以下是Cast實體提取示例:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Cast" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
NSArray *sortDescriptors = @[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
// Set predicate
NSPredicate *requestPredicate = [NSPredicate predicateWithFormat:@"SUBQUERY(movies, $m, ANY $m.genres.name == %@).@count != 0 AND SUBQUERY(movies, $m, SUBQUERY($m.genres, $g, ANY $g.theaters.name == %@).@count != 0).@count != 0", @"Action", @"Harkins"];
[fetchRequest setPredicate:requestPredicate];
// Fetch
NSError *error = nil;
if (![aFetchedResultsController performFetch:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
}
// Check fetched objects
NSArray *fetchedObjects = [aFetchedResultsController fetchedObjects];
for (Cast *eachCast in fetchedObjects) {
NSLog(@"Each Cast name: %@", eachCast.name);
}
只需用所需的流派名稱替換@“Action”,用劇院名稱替換@“Harkins”。
以下是我設置核心數據模型的方法:
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