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我正試圖優化針對核心數據的提取請求。針對最近修改的對象優化的核心數據提取
我有一個名爲lastModifiedDate屬性的實體,它是一個NSDate對象。我需要查詢我的數據庫中最新的lastModifiedDate屬性。我有下面的代碼,它可以在小數據集中正常工作,但是有一個擁有40k記錄的數據庫,這個查詢就像廢話一樣運行。
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;