Core Data NSExpression Error
Core Data NSExpression Error
- Subject: Core Data NSExpression Error
- From: Chris Tracewell <email@hidden>
- Date: Tue, 11 May 2010 18:50:09 -0700
I am on OS X 10.6, XCode 3.2.2, GC and Core Data. I have a single entity app where I subclassed NSManagedObject so I can generate a "Job Ticket ID" for my Job entity whenever a new Job is inserted. However I am getting an error in my Log that is complaining that...
-[NSCFNumber count]: unrecognized selector sent to instance 0x20001ab40
The property I am trying to get the max value for is defined as a 16 Integer. The code is below and was taken from "Fetching Specific Values" @ http://developer.apple.com/mac/library/documentation/cocoa/conceptual/CoreData/Articles/cdFetching.html#//apple_ref/doc/uid/TP40002484-SW1
-(void)awakeFromInsert
{
NSFetchRequest *theRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *theEntity = [NSEntityDescription entityForName:@"TKJob" inManagedObjectContext:[self managedObjectContext]];
[theRequest setEntity:theEntity];
[theRequest setResultType:NSDictionaryResultType];
// Create an expression for the key path.
NSExpression *theKeyPathExpression = [NSExpression expressionForKeyPath:@"myID"];
NSExpression *theMaxExpression = [NSExpression expressionForFunction:@"max:" arguments:[NSArray arrayWithObject:theKeyPathExpression]];
// Create an expression description using the theMaxExpression and returning a Number.
NSExpressionDescription *theExpressionDescription = [[NSExpressionDescription alloc] init];
[theExpressionDescription setName:@"maxID"];
[theExpressionDescription setExpression:theMaxExpression];
[theExpressionDescription setExpressionResultType:NSInteger16AttributeType];
[theRequest setPropertiesToFetch:[NSArray arrayWithObject:theExpressionDescription]];
// Execute the fetch.
NSError *theError;
NSArray *theResultsArray = [[self managedObjectContext] executeFetchRequest:theRequest error:&theError];
if (theResultsArray == nil)
{
// Handle the error.
}
else
{
if ([theResultsArray count] > 0)
{
// do some math and set myID to maxID + 1
}
}
}
Any thoughts?_______________________________________________
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