StackOverflow2013

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copied!<blockquote> <blockquote> <p>Can this be done with one Fetch Request or would I do 2 Requests and then merge them?<br/></p> </blockquote> </blockquote> <p>Yes it can be done with one request. <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html#//apple_ref/doc/uid/TP40002484-SW6" rel="nofollow noreferrer">see here</a></p> <pre><code>/*UNTESTED*/ - (NSNumber*) billingSumForClient:(NSManagedObjectID*)clientId context:(NSManagedObjectContext*)context { NSNumber* total = nil; NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Billing"]; [request setResultType:NSDictionaryResultType]; NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"amount"]; NSExpression *sumExpression = [NSExpression expressionForFunction:@"sum:" arguments:[NSArray arrayWithObject:keyPathExpression]]; NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init]; [expressionDescription setName:@"total"]; [expressionDescription setExpression:sumExpression]; [expressionDescription setExpressionResultType:NSDateAttributeType]; [request setPredicate:[NSPredicate predicateWithFormat:@"client == %@",clientId]]; [request setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]]; NSError *error = nil; NSArray *objects = [context executeFetchRequest:request error:&error]; if (&error) { // Handle the error. } else { if ([objects count] > 0) { total = [[objects objectAtIndex:0] valueForKey:@"total"]; } } return total; } </code></pre> <blockquote> <blockquote> <p>Can I somehow use valueForKey:@"billing.@sum.amount"?<br/></p> </blockquote> </blockquote> <p>Yes. <a href="https://stackoverflow.com/questions/7565425/core-data-get-sum-of-values-fetched-properties-vs-propagation">see here(@Daniel link)</a><br/> This might be faster if all your billings are already faulted into your current context.</p>

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