用于比较核心数据日期属性的月份组件的谓词

您可以在您的实体上创建一个新方法,我们将调用它 monthOfDate . 此方法只使用 [self dateAttribute] 和 NSDateComponents 提取日期的月份。

然后您可以编写一个谓词:

//assuming 1-based month indexing
NSPredicate * julyEntities = [NSPredicate predicateWithFormat:@"monthOfDate = 7"]; 

这里的技巧是认识到谓词的左键路径将导致方法调用。因此,如果将左键路径设置为“monthofdate”,它最终将调用 月历 方法,并使用方法的返回值作为谓词中的比较值。整洁!

还不能评论,所以请这样问。

你是怎么做到的?我试图在托管对象类中添加一个方法,但一旦谓词激发,它就说它找不到keypath monthofdate?

用两个文件更新:

h文件:

@property (nonatomic,retain) NSNumber *monthOfDate;
-(NSNumber *)monthOfDate;

m文件:

@synthesize monthOfDate;

-(NSNumber *) monthOfDate
{
NSDate *date = [self start];
NSDateComponents *components = [[NSCalendar currentCalendar]components: NSCalendarUnitMonth fromDate:date];
NSNumber *month = [NSNumber numberWithInteger:[components month]];
return month;
}

更新2

上面的代码位于自动生成的事件类(nsmanaged对象)中。稍后我可能会将我的自定义代码移到一个类别中,但到目前为止,不需要修改模型。

下面是带有上述谓词的FetchedResultsController(在uiviewController类中)设置:

nsfetchRequest*fetchRequest=[[nsfetchRequest alloc]init];

NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"Event" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];

NSSortDescriptor *sortfix = [[NSSortDescriptor alloc]initWithKey:@"timeStamp" ascending:NO];
[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:sortfix,nil]];
[fetchRequest setFetchBatchSize:20];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"client == %@ AND monthOfDate = %d", clientMO,[NSNumber numberWithInteger:6]];
[fetchRequest setPredicate:predicate];


NSFetchedResultsController *theFetchedResultsController =

[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:managedObjectContext sectionNameKeyPath:sectionKeyPathProperty
                                               cacheName:nil];

//sectionKeyPathProperty is a variable that let's me choose one of multiple transient properties I have created for creating relevant sections.

self.fetchedResultsControllerClient = theFetchedResultsController;
_fetchedResultsControllerClient.delegate = self;

return _fetchedResultsControllerClient;