Re: Core Data Predicate Builder - comparing dates
Re: Core Data Predicate Builder - comparing dates
- Subject: Re: Core Data Predicate Builder - comparing dates
- From: Steve Cronin <email@hidden>
- Date: Sat, 29 Aug 2009 23:45:42 -0500
Ben;
Thanks for taking the time to respond.
I believe that I was blinded by a build issue in my allegation that
the Predicate Builder mechanism was not giving correct results.
This seems to be working fine now.
I'm glad you have expressed the fragility issue on equivalence - I'll
remember that.
Thanks for the predicate in code.
It's amazing how often the Cocoa answers are simple and
straightforward when you finally see them.
I might suggest the predicate you cited be considered for inclusion in
the Apple documentation somewhere.
Most (all?) the examples use operators and some fixed value.
I know it may seem obvious (it does seem obvious now) but, when you
don't know, a range of different examples can be a godsend...
Thank-you!
Steve
On Aug 29, 2009, at 7:35 PM, Ben Trumbull wrote:
I have a Core Data entity that has a dateCreated and a dateModified -
both NSDates in the object files.
I'd like to construct a predicate that will retrieve all records
where
a record's dateModified is greater than that record's dateCreated.
Its deceptively easy to setup something that looks like it should
work
using 'Control-click' and 'Key' in the predicate builder in XCode.
But when I run queries it doesn't appear to yield the right results.
My thinking is that the comparison operators don't properly evaluate
dates (am I wrong?)
Comparison operators work just fine on dates, although == and != are
fragile since NSDates are double time stamps, and floating point
numbers have odd == behavior.
What does the predicate look like ? How is it not working ? What
does SQL logging show ?
So dropping back to code - how would I write this predicate in code?
[NSPredicate predicateWithFormat:@"dateModified > dateCreated"]
- Ben
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