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我正试图优化针对核心数据的提取请求。针对最近修改的对象优化的核心数据提取
我有一个名为lastModifiedDate属性的实体,它是一个NSDate对象。我需要查询我的数据库中最新的lastModifiedDate属性。我有下面的代码,它可以在小数据集中正常工作,但是有一个拥有40k记录的数据库,这个查询就像废话一样运行。
NSDate *mostRecentLastModifiedDate = nil;
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:entityName inManagedObjectContext:self.managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
[request setFetchLimit:1];
[request setPropertiesToFetch:[NSArray arrayWithObject:@"lastModifiedDate"]];
NSSortDescriptor *dateSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lastModifiedDate" ascending:NO];
[request setSortDescriptors:[NSArray arrayWithObject:dateSortDescriptor]];
[dateSortDescriptor release];
NSError *error = nil;
NSArray *result = [self.managedObjectContext executeFetchRequest:request error:&error];
if (error) {
NSLog(@"Error fetching most recent lastModifiedDate property for %@ entity, error details: %@", entityName, error);
} else if ([result count] > 0) {
mostRecentLastModifiedDate = [[[[result objectAtIndex:0] valueForKey:@"lastModifiedDate"] copy] autorelease];
} else {
mostRecentLastModifiedDate = [NSDate distantPast];
}
[request release];
return mostRecentLastModifiedDate;