Question

I have an entity with an attribute date which is an NSDate. How would I construct a predicate to get the earliest date stored in the model?

I want to be able to calculate the number of days between now and the earliest date in the entity you see so I can lay them out in a tableview one day at a time. This bit I’m sure I can do myself.

Thanks for all your help.

Answer 1

Construct an NSExpression to retrieve the minimum date. Something like the following:

NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:@"date"];
NSExpression *minDateExpression = [NSExpression expressionForFunction:@"min:"
    arguments:[NSArray arrayWithObject:keyPathExpression]];

You can then wrap this in an NSExpressionDescription, call setPropertiesToFetch: on your request, and execute it as normal. Instead of returning an array of managed objects, it will now return a dictionary containing the result of your expression—the minimum date.

See the Fetching Specific Values section of Apple’s Core Data Programming Guide for a more detailed explanation and sample code.