Re: Core Data Predicate Question
Re: Core Data Predicate Question
- Subject: Re: Core Data Predicate Question
- From: Indragie Karunaratne <email@hidden>
- Date: Fri, 08 Jul 2011 19:48:42 -0600
Awesome, thank you. For anyone else who stumbles upon this question looking for something similar, check out Apple's DerivedProperty example:
http://developer.apple.com/library/mac/#samplecode/DerivedProperty/Introduction/Intro.html
It has examples on using the <= & > string comparison trick as well as normalizing strings for indexing.
On 2011-07-08, at 2:40 PM, The Karl Adam wrote:
> Well, when I said ANY, I really meant "IN termsArray", but for the
> partial matches that you want your approach is fine, you'll just want
> to use > & <= with character evaluations to speed this up. Check the
> 2010 CoreData Performance session from WWDC for more details, but it's
> a standard SQL trick to speed up string comparisons.
>
> _Karl
>
> On Thu, Jul 7, 2011 at 10:38 AM, Indragie Karunaratne
> <email@hidden> wrote:
>> I came up with this code earlier:
>> NSArray *searchTerms = [cleanedQuery componentsSeparatedByString:@" "];
>> NSPredicate *basePredicate = [NSPredicate
>> predicateWithFormat:@"SUBQUERY(keywords, $keyword, $keyword.name BEGINSWITH
>> $QUERY).@count != 0"];
>> NSMutableArray *subpredicates = [NSMutableArray array];
>> for (NSString *searchTerm in searchTerms) {
>> NSDictionary *sub = [NSDictionary
>> dictionaryWithObjectsAndKeys:searchTerm, @"QUERY", nil];
>> NSPredicate *termPredicate = [basePredicate
>> predicateWithSubstitutionVariables:sub];
>> [subpredicates addObject:termPredicate];
>> }
>> NSPredicate *combinedPredicate = [NSCompoundPredicate
>> andPredicateWithSubpredicates:subpredicates];
>>
>> This doesn't use "ANY" as you mentioned (not sure exactly how I would use
>> that) but it works. However, I'm sure there's a better way to simplify this
>> instead of using a giant compound AND predicate to match each one of the
>> search terms. Is there any way to simplify this?
>> Thanks
>> On 2011-07-07, at 11:23 AM, The Karl Adam wrote:
>>
>> You want to be using SUBQUERY() to match ANY keywords. Check the docs
>> for the predicate reference details for this.
>>
>> _Karl
>>
>> On Wed, Jul 6, 2011 at 8:23 PM, Indragie Karunaratne
>> <email@hidden> wrote:
>>
>> Hi all,
>>
>> I have a Core Data object model that I'm trying to write a fetch predicate
>> for (to use for search). Quick explanation of the model:
>>
>> We'll call the main entity "Book". There's also a "Keyword" entity. The
>> Book entity has a to-many relationship with the Keyword entity called
>> "keywords". In turn, the Keyword entity has an inverse relationship with the
>> Book entity called "book". The Keyword entity has a single attribute called
>> "name". So basically, each Book has Keywords that describe it.
>>
>> For my search, I have an array of search terms. I need a predicate that I
>> can use on fetch requests for the Book entity that will evaluate to TRUE if
>> ALL of the search terms have a corresponding Keyword in that the "name"
>> property begins with the search term.
>>
>> For example:
>>
>> There are three books:
>>
>> Book1 - keywords: {"fiction", "scifi"}
>>
>> Book2 - keywords: {"nonfiction"}
>>
>> If the search terms were {"fic", "nonfic", "sci"} the resulting fetched
>> array would contain NOTHING because none of the books have keywords that
>> begin with all 3 of those search terms..
>>
>> However, if the search terms were {"fic", "sci"}, the resulting fetched
>> array would contain Book1 since its keywords "fiction" and "scifi" begin
>> with the two search terms "fic" and "sci". The key part here is that ALL of
>> the search terms have to have a corresponding keyword as demonstrated above
>> for the predicate to evaluate to true.
>>
>> I hope I've explained this problem well enough, it's hard to put this stuff
>> into words ;-)
>>
>> Any help is appreciated,
>>
>> Indragie_______________________________________________
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