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Re: using SUBQUERY to remove nulls
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Re: using SUBQUERY to remove nulls


  • Subject: Re: using SUBQUERY to remove nulls
  • From: Keary Suska <email@hidden>
  • Date: Wed, 05 Jun 2013 15:34:00 -0600

On Jun 5, 2013, at 7:50 AM, Roland King wrote:

> I have a property, 'meaning' on my objects in a core data model. It's optional. I need to find all the meanings which contain a certain string (not terribly efficient but a fairly rare search).
>
> I started out with this predicate
>
> 	[ NSPredicate predicateWithFormat:@"meaning CONTAINS %@", searchString ];
>
> but it crashes with a EXC_BAD_ACCESS deep down in the SQLLite execution trying to evaluate CFStringGetLength on a zero pointer. My assumption here is that it's finding an object with a null meaning, so I want to filter them out. So I tried
>
> 	[ NSPredicate predicateWithFormat:@"( meaning != NULL ) AND ( meaning CONTAINS %@ )", searchString ];
>
> and a few variants thereof, but they crash the same way, leading me to think perhaps both parts of the AND are evaluated whether or not the first part succeeds, ie not like C's guaranteed shortcut, and perhaps I shouldn't expect it to be.

I would not jump to an issue with NULL values since NULL handing is fundamental to any SQL-aware API. I would instead consider a memory issue first. Turn on zombies and see if you get a different response. Post the backtrace if you want potentially better feedback. In any case, it is highly unlikely to be the predicate or underlying SQL machinery that is causing this crash.

HTH,

Keary Suska
Esoteritech, Inc.



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