所以,基本上,您想要获取特定文件夹中的所有项目(即,您希望具有给定folderName和groupName ...的所有项目唯一标识特定文件夹)。
既然你说你已经有了关系,我会假设他们是以反向关系设置的。
此外,我将假定一个项目具有名为“文件夹”的一对一关系,该关系是该项目所在的文件夹。该文件夹将具有该项目文件夹中项目的多对多关系“项目”。
因此,以下将是许多方法来完成你想要的东西之一。
- (NSSet*)getItemsForFolderName:(NSString*)folderName
groupName:(NSString*)groupName
inMOC:(NSManagedObjectContext*)moc
error:(NSError**)error {
NSSet *result = nil;
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Folder"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"folderName = %@ AND groupName = %@", folderName, groupName];
fetchRequest.relationshipKeyPathsForPrefetching = @[@"items"];
NSArray *folders = [moc executeFetchRequest:fetchRequest error:error];
if (folders) {
result = [[folders firstObject] items];
}
return result;
}
您也可以简单地获取项目。至于哪个最好,这取决于你如何拥有你的属性索引,以及你正在做什么类型的其他提取。
- (NSArray*)getItemsForFolderName:(NSString*)folderName
groupName:(NSString*)groupName
inMOC:(NSManagedObjectContext*)moc
error:(NSError**)error {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"folderName = %@ AND folder.groupName = %@", folderName, groupName];
return [moc executeFetchRequest:fetchRequest error:error];
}
编辑
JamEngulfer221,我敢肯定这些例子会的工作,但因为你说他们甚至没有经过我指出在您的文章中的错误,我想我会砍一个快速的项目和测试...我老了,有时忘记的东西...
所以,我砍了一个测试,用下面的代码。
首先,创建模型...
- (NSManagedObjectModel *)makeModel {
NSEntityDescription *group = [[NSEntityDescription alloc] init];
group.name = @"Group";
NSAttributeDescription *groupName = [[NSAttributeDescription alloc] init];
groupName.name = @"groupName";
groupName.attributeType = NSStringAttributeType;
NSEntityDescription *folder = [[NSEntityDescription alloc] init];
folder.name = @"Folder";
NSAttributeDescription *folderName = [[NSAttributeDescription alloc] init];
folderName.name = @"folderName";
folderName.attributeType = NSStringAttributeType;
NSEntityDescription *item = [[NSEntityDescription alloc] init];
item.name = @"Item";
NSAttributeDescription *itemName = [[NSAttributeDescription alloc] init];
itemName.name = @"itemName";
itemName.attributeType = NSStringAttributeType;
NSRelationshipDescription *folderToGroupRelationship = [[NSRelationshipDescription alloc] init];
NSRelationshipDescription *groupToFoldersRelationship = [[NSRelationshipDescription alloc] init];
groupToFoldersRelationship.name = @"folders";
groupToFoldersRelationship.destinationEntity = folder;
groupToFoldersRelationship.minCount = 0;
groupToFoldersRelationship.maxCount = 0;
groupToFoldersRelationship.deleteRule = NSCascadeDeleteRule;
groupToFoldersRelationship.inverseRelationship = folderToGroupRelationship;
folderToGroupRelationship.name = @"group";
folderToGroupRelationship.destinationEntity = group;
folderToGroupRelationship.minCount = 0;
folderToGroupRelationship.maxCount = 1;
folderToGroupRelationship.deleteRule = NSNullifyDeleteRule;
folderToGroupRelationship.inverseRelationship = groupToFoldersRelationship;
NSRelationshipDescription *folderToItemsRelationship = [[NSRelationshipDescription alloc] init];
NSRelationshipDescription *itemToFolderRelationship = [[NSRelationshipDescription alloc] init];
folderToItemsRelationship.name = @"items";
folderToItemsRelationship.destinationEntity = item;
folderToItemsRelationship.minCount = 0;
folderToItemsRelationship.maxCount = 0;
folderToItemsRelationship.deleteRule = NSCascadeDeleteRule;
folderToItemsRelationship.inverseRelationship = itemToFolderRelationship;
itemToFolderRelationship.name = @"folder";
itemToFolderRelationship.destinationEntity = folder;
itemToFolderRelationship.minCount = 0;
itemToFolderRelationship.maxCount = 1;
itemToFolderRelationship.deleteRule = NSNullifyDeleteRule;
itemToFolderRelationship.inverseRelationship = folderToItemsRelationship;
group.properties = @[groupName, groupToFoldersRelationship];
folder.properties = @[folderName, groupName, folderToGroupRelationship, folderToItemsRelationship];
item.properties = @[itemName, folderName, itemToFolderRelationship];
NSManagedObjectModel *model = [[NSManagedObjectModel alloc] init];
model.entities = @[group, folder, item];
return model;
}
而且搜索方法...
- (NSArray*)getItemsForFolderName:(NSString*)folderName
groupName:(NSString*)groupName
inMOC:(NSManagedObjectContext*)moc
error:(NSError**)error {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"folderName = %@ AND folder.groupName = %@", folderName, groupName];
return [moc executeFetchRequest:fetchRequest error:error];
}
并且测试...
- (void)testBlarg {
NSManagedObjectModel *model = [self makeModel];
NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];
[psc addPersistentStoreWithType:NSInMemoryStoreType configuration:nil URL:nil options:nil error:NULL];
NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
moc.persistentStoreCoordinator = psc;
for (int g = 0; g < 10; ++g) {
NSManagedObject *group = [NSEntityDescription insertNewObjectForEntityForName:@"Group" inManagedObjectContext:moc];
NSString *groupName = [NSString stringWithFormat:@"Group %02d", g];
[group setValue:groupName forKey:@"groupName"];
for (int f = 0; f < 10; ++f) {
NSManagedObject *folder = [NSEntityDescription insertNewObjectForEntityForName:@"Folder" inManagedObjectContext:moc];
NSString *folderName = [NSString stringWithFormat:@"Folder %02d", f];
[folder setValue:folderName forKey:@"folderName"];
[folder setValue:groupName forKey:@"groupName"];
[folder setValue:group forKey:@"group"];
for (int i = 0; i < 10; ++i) {
NSManagedObject *item = [NSEntityDescription insertNewObjectForEntityForName:@"Item" inManagedObjectContext:moc];
NSString *itemName = [NSString stringWithFormat:@"Item %02d (%@;%@)", i, folderName, groupName];
[item setValue:itemName forKey:@"itemName"];
[item setValue:folderName forKey:@"folderName"];
[item setValue:folder forKey:@"folder"];
}
}
}
[moc save:NULL];
[moc reset];
NSString *folderName = @"Folder 04";
NSString *groupName = @"Group 02";
NSArray *items = [self getItemsForFolderName:folderName groupName:groupName inMOC:moc error:NULL];
items = [items sortedArrayUsingDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"itemName" ascending:YES]]];
XCTAssertEqual(10, items.count);
for (int i = 0; i < 10; ++i) {
NSManagedObject *object = items[i];
NSString *expectedItemName = [NSString stringWithFormat:@"Item %02d (%@;%@)", i, folderName, groupName];
XCTAssertEqualObjects(expectedItemName, [object valueForKey:@"itemName"]);
NSManagedObject *folder = [object valueForKey:@"folder"];
XCTAssertEqualObjects(folderName, [folder valueForKey:@"folderName"]);
XCTAssertEqualObjects(groupName, [folder valueForKey:@"groupName"]);
NSManagedObject *group = [folder valueForKey:@"group"];
XCTAssertEqualObjects(groupName, [group valueForKey:@"groupName"]);
}
}
是item.folderName的其包含文件夹的名称和item.folder.folderName相同? – Willeke
如果你有关系,你为什么不使用它们? – quellish
@Willeke,是的。冷静,因为我不知道如何和我被可用的文件混淆。 – JamEngulfer