如何找到存储在coredata中的日期的最大值？

Question

我在 coredata 中创建了一个实体，它包含一个 Date 类型的属性。那么我怎样才能找到存储在那里的日期的最大值。

Answer 1

NSString * yourEntityName = @"Entity";
NSString * yourDateAttributeName = @"date";

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

NSEntityDescription *entity = [NSEntityDescription entityForName:yourEntityName
                                          inManagedObjectContext:ctx];
[fetchRequest setEntity:entity];
[fetchRequest setPropertiesToFetch:@[yourDateAttributeName]];
[fetchRequest setFetchLimit:1];

// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:yourDateAttributeName ascending:NO];
NSArray *sortDescriptors = @[sortDescriptor];

[fetchRequest setSortDescriptors:sortDescriptors];

NSError * error = nil;
NSArray * results = [ctx executeFetchRequest:fetchRequest error:&error];

NSManagedObject * yourEntityObject = [results firstObject];

NSDate * date = [yourEntityObject valueForKey:yourDateAttributeName];