与核心数据
问题描述:
关系撷取实体我在我的核心数据的数据库Person
2个实体和Photo
一个Person
与Photo
一个To-Many
关系,Photo
有Person
(Person<-->>Photo)
反向关系。我通过以下方式将我的应用程序的一些初始数据加载到.plist中:与核心数据
-(void)populateDataStorage{
NSString *path = [[NSBundle mainBundle] pathForResource:@"FakeData" ofType:@"plist"];
if(path){
NSArray *plistData = [[NSArray alloc] initWithContentsOfFile:path];
NSEnumerator *enumerator = [plistData objectEnumerator];
NSArray *personResults;
Photo *photo;
Person *person;
id currItem = [enumerator nextObject];
while (currItem != nil) {
photo = (Photo *)[NSEntityDescription insertNewObjectForEntityForName:@"Photo" inManagedObjectContext:[flickrFetcher managedObjectContext]];
photo.name = [currItem objectForKey:@"name"];
photo.path = [currItem objectForKey:@"path"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name = %@", [currItem objectForKey:@"user"]];
personResults = [flickrFetcher fetchManagedObjectsForEntity:@"Person" withPredicate:predicate];
if ([personResults count] > 0) {
person = [personResults objectAtIndex:0];
}
else {
person = (Person *)[NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:[flickrFetcher managedObjectContext]];
person.name = [currItem objectForKey:@"user"];
}
photo.person = person;
[person addPhotosObject:photo];
NSLog(@"Photo %@ added for user %@", photo.name, person.name);
currItem = [enumerator nextObject];
}
[plistData release];
}
}
一切正常加载。然后我使用NSFetchedResultsController
获取Person
并加载UITableView
,这一切都可行。当用户点击该属于用户的小区我必须加载另一个UITableView
与选定人员的照片,这样我就在我的UITableViewController我的照片的表视图如下:
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"person = %@", person];
self.fetchedResultsController = [[FlickrFetcher sharedInstance] fetchedResultsControllerForEntity:@"Photo" withPredicate:predicate];
}
return self;
}
在我viewDidLoad
:
- (void)viewDidLoad
{
[super viewDidLoad];
NSError *error = nil;
[fetchedResultsController performFetch:&error];
for(Photo *photo in person.photos){
NSLog(@"Photo %@ belongs to %@", photo.name, person.name);
}
NSLog(@"Photo count %d", [[fetchedResultsController fetchedObjects] count]);
}
计数是给我的0,我从来没有这个人的照片,但我知道他们是正确保存,因为它们都打印出在Person
传递。任何想法我可能做错了什么?
在我FlickrFetcher
类获得NSFetchedResultsController
编辑
实用方法:
- (NSFetchedResultsController *)fetchedResultsControllerForEntity:(NSString*)entityName withPredicate:(NSPredicate*)predicate {
NSFetchedResultsController *fetchedResultsController;
/*
Set up the fetched results controller.
*/
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName 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 = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Add a predicate if we're filtering by user name
if (predicate) {
[fetchRequest setPredicate:predicate];
}
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[self managedObjectContext] sectionNameKeyPath:nil cacheName:@"Root"];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptors release];
return [fetchedResultsController autorelease];
}
我在我UITableViewController
创建自己的NSFetchedResultsController
:
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Photo" inManagedObjectContext:[flickFetcher managedObjectContext]];
[request setEntity:entity];
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:descriptor, nil];
[request setSortDescriptors:sortDescriptors];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"person = %@", person];
[request setPredicate:predicate];
fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:[flickFetcher managedObjectContext] sectionNameKeyPath:nil cacheName:@"Root"];
[request release];
[descriptor release];
[sortDescriptors release];
NSError *error = nil;
[fetchedResultsController autorelease];
[fetchedResultsController performFetch:&error];
我看不出区别。
答
看不到任何事情。插入所有测试数据后,我想在上下文中插入保存。 (而不是周围的下一次插入。)
一个评论:
photo.person = person;
[person addPhotosObject:photo];
这是多余的。如果您设置了另一个关系,那么在核心数据中与反向关系建模的关系将正确设置反向关系。所以,只需要其中的一条。
感谢您的提示,我设法从上下文中检索照片,这很奇怪,因为我所做的只是创建自己的提取结果控制器,这与我之前使用的实用程序方法没有什么不同,但现在表格单元格不再是' t设置,cellForRowAtIndex永远不会因为某种原因被调用,我将更新代码以显示两个fetchedResultsControllers。 – 8vius
没有cellForRowAtIndex:=没有tableView.dataSource,或numberOfRowsInSection = 0 – bshirley
是numberOfRowsInSection交易,这没有把戏。注意我的fetchedResultsControllers有什么不同?除了升序参数 – 8vius