Core Data: trying to find minimum date for an attribute in an entity

Question

I'm trying to find the oldest date in a particular attribute in Core Data. I've found an example in the Core Data Programming Guide that purports to do exactly that, but keep getting an unrecognized selected error when I run it.

My code (with only minimal changes from the Apple Example):

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Session" inManagedObjectContext: ctx];
[request setEntity:entity];

// Specify that the request should return dictionaries.
[request setResultType:NSDictionaryResultType];

// Create an expression for the key path.
NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"startedAt"];

// Create an expression to represent the minimum value at the key path 'creationDate'
NSExpression *minExpression = [NSExpression expressionForFunction:@"min:" arguments:[NSArray arrayWithObject:keyPathExpression]];

// Create an expression description using the minExpression and returning a date.
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];

// The name is the key that will be used in the dictionary for the return value.
[expressionDescription setName:@"minDate"];
[expressionDescription setExpression:minExpression];
[expressionDescription setExpressionResultType:NSDateAttributeType];

// Set the request's properties to fetch just the property represented by the expressions.
[request setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];

// Execute the fetch.
NSError *error;
NSArray *objects = [ctx executeFetchRequest:request error:&error];

And the error:

-[NSCalendarDate count]: unrecognized selector sent to instance ...

Which is strange given that 1) NSCalendarDate is deprecated and 2) I'm definitely not calling count.

Any help would be most appreciated!

Answer 1

Why not just add a sort descriptor to sort by startedDate ascending, and then only have the fetch request return 1 object?