自定义Core数据SectionNameKeyPath [英] Custom Core Data SectionNameKeyPath
问题描述
我是新的核心数据，我试图找出如何创建自定义 sectionNameKeyPath 在我的 NSFetchedResultsController 。我有一个具有属性 acctPeriod 的managed对象。它是一个 NSString 。我想根据此字段的前4个字符创建节。前4个字符表示会计期间的年份，不需要保存。
我已经浏览了这个网站，看到了关于临时属性的帖子，但我似乎不能让他们工作。基本上我想要这个，然后为 sectionNameKeyPath 分配 periodYear 。
@dynamic periodYear;
- （NSString *）periodYear
{
return [self.acctPeriod substringToIndex：4];
}
任何帮助将不胜感激。
**更新：
使用Martin R.答案，我能够按预期工作。
- （NSFetchedResultsController *）fetchedResultsController
{
if（_fetchedResultsController！= nil）{
return _fetchedResultsController;
}
NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
//适当地编辑实体名称。
NSEntityDescription * entity = [NSEntityDescription entityForName：@BillinginManagedObjectContext：self.managedObjectContext];
[fetchRequest setEntity：entity];
//将批量大小设置为合适的数量。
[fetchRequest setFetchBatchSize：20];
//根据需要编辑排序键。
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@acctPeriodascending：NO];
NSArray * sortDescriptors = @ [sortDescriptor];
//谓词
NSPredicate * pred = [NSPredicate predicateWithFormat：@clients =％@，self.client];
NSLog（@％@，pred）;
// [fetchRequest setResultType：NSDictionaryResultType];
// [fetchRequest setReturnsDistinctResults：YES];
[fetchRequest setPredicate：pred];
[fetchRequest setSortDescriptors：sortDescriptors];
NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：self.managedObjectContext sectionNameKeyPath：@periodYearcacheName：nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError * error = nil;
if（！[self.fetchedResultsController performFetch：& error]）
{
NSLog（@Unresolved error％@，％@，error，[error userInfo]）;
abort（）;
}
return _fetchedResultsController;
}
在您的托管对象子类的类扩展中的 periodYear 方法（将使用
作为节名称键路径）：
@interface事件（AdditionalMethods）
- （NSString *）periodYear;
@end
@implementation事件（AdditionalMethods）
- （NSString *）periodYear {
return [self.acctPeriod substringToIndex：4];
}
@end
确保 acctPeriod 用作提取请求的第一个（或唯一）排序描述符：
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@acctPeriodascending：YES];
NSArray * sortDescriptors = @ [sortDescriptor];
[fetchRequest setSortDescriptors：sortDescriptors];
使用 periodYear 为 sectionNameKeyPath 用于获取的结果控制器：
NSFetchedResultsController * _fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest：fetchRequest
managedObjectContext：self.managedObjectContext
sectionNameKeyPath：@periodYear
cacheName：nil];
_fetchedResultsController.delegate = self;
self.fetchedResultsController = _fetchedResultsController;
最后添加默认的 titleForHeaderInSection
- （NSString *）tableView：（UITableView *）tableView titleForHeaderInSection：（NSInteger）section {
id& NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex：section];
return [sectionInfo name];
}
或者，您可以定义 periodYear 作为管理对象的 transient属性。
在这种情况下，它也不会存储在数据库中，但可以按照需要计算并缓存的方式实现。
来自Apple开发人员库的 DateSectionTitles 示例项目演示了如何工作。 p>
I am new at core data and am trying to figure out how to create a custom sectionNameKeyPath in my NSFetchedResultsController. I have a managed object with an attribute called acctPeriod. It is a NSString. I want to create sections based on the first 4 characters of this field. The first 4 characters represent the year of the accounting period and doesn't need to be saved.
I have gone through this site and have seen posts about transient attributes but I can't seem to get them to work. Basically I want this and then assign periodYear for my sectionNameKeyPath.
@dynamic periodYear;
-(NSString *)periodYear
{
return [self.acctPeriod substringToIndex:4];
}
Any help would be appreciated.
**UPDATE: Using Martin R. answer, I was able to get it to work as expected.
- (NSFetchedResultsController *)fetchedResultsController
{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Billing" 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:@"acctPeriod" ascending:NO];
NSArray *sortDescriptors = @[sortDescriptor];
//Predicate
NSPredicate *pred = [NSPredicate predicateWithFormat:@"clients = %@", self.client];
NSLog(@"%@",pred);
//[fetchRequest setResultType:NSDictionaryResultType];
//[fetchRequest setReturnsDistinctResults:YES];
[fetchRequest setPredicate:pred];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"periodYear" cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error])
{
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _fetchedResultsController;
}
The following should work: Implement the periodYear method (which will be used
as "section name key path") in a class extension of your managed object subclass:
@interface Event (AdditionalMethods)
- (NSString *)periodYear;
@end
@implementation Event (AdditionalMethods)
- (NSString *)periodYear {
return [self.acctPeriod substringToIndex:4];
}
@end
Make sure that acctPeriod is used as the first (or only) sort descriptor for the fetch request:
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"acctPeriod" ascending:YES];
NSArray *sortDescriptors = @[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
Use periodYear as sectionNameKeyPath for the fetched results controller:
NSFetchedResultsController *_fetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:fetchRequest
managedObjectContext:self.managedObjectContext
sectionNameKeyPath:@"periodYear"
cacheName:nil];
_fetchedResultsController.delegate = self;
self.fetchedResultsController = _fetchedResultsController;
And finally add the default titleForHeaderInSection method:
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
return [sectionInfo name];
}
Alternatively, you can define periodYear as transient attribute of the managed object.
It will also not be stored in the database in that case, but can be implemented in a way that the value is calculated on demand and cached.
The DateSectionTitles sample project from the Apple Developer Library demonstrates how this works.
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