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POnsexpression with custom function core data
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copied!<p>i'm trying to group and count on date on a core data entity. since date cant be group due to different time. so i'm trying to pass custom function to nsexpression. but i get some errors i dont know what's the correct way to do it.</p> <p>code for grouping and counting:</p> <pre><code>NSEntityDescription *entity = [NSEntityDescription entityForName:@"TEvents" inManagedObjectContext:context]; NSDictionary *props = [entity propertiesByName]; NSPropertyDescription *propDesc3 = [props objectForKey:@"startDateTime"]; NSExpression *propExpr3 = [NSExpression expressionForKeyPath:@"startDateTime"]; NSExpression *countExpr3 = [NSExpression expressionForFunction:propExpr3 selectorName:@"dateShort" arguments:nil]; NSExpressionDescription *exprDesc3 = [[NSExpressionDescription alloc] init]; [exprDesc3 setExpression:countExpr3]; [exprDesc3 setExpressionResultType:NSDateAttributeType]; [exprDesc3 setName:@"dateStart"]; NSFetchRequest *fr = [NSFetchRequest fetchRequestWithEntityName:@"TEvents"]; [fr setPropertiesToGroupBy:[NSArray arrayWithObjects:propDesc3, nil]]; [fr setPropertiesToFetch:[NSArray arrayWithObjects:propDesc3, exprDesc3, nil]]; [fr setResultType:NSDictionaryResultType]; NSError * error = nil; NSArray *results = [context executeFetchRequest:fr error:&error]; </code></pre> <p>dateShort is a nsdate category function which converts datatime to user's current zone:</p> <pre><code>-(NSString *) dateShort { NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setCalendar:[NSCalendar currentCalendar]]; [formatter setTimeZone:[NSTimeZone localTimeZone]]; [formatter setDoesRelativeDateFormatting:YES]; [formatter setDateStyle:NSDateFormatterShortStyle]; [formatter setTimeStyle:NSDateFormatterNoStyle]; NSString *tmpValue = [formatter stringFromDate:self]; return tmpValue; } </code></pre> <p>error:</p> <blockquote> <p>Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unsupported function type passed to SQL store'</p> </blockquote> <p>how to achieve this goal: convert datetime to current zone and group and count on (yy-mm-dd) on a core data entity?</p>

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