When searching for text snippets in sql databases you might want to rank the results according to “how good did it match”. And: the ranking shouldn’t make the query slower.
Let’s take a simple example using the LIKE operator. (I know, FTS does a better job, but let’s stick to like for now).
Assume the search …
Gestern gab’s einen Mini-Vortrag von mir bei den CocoaHeads München:
CoreData (iOS) ist nur mit Tricks dazu zu bringen den Index bei Textsuche zu benutzen,
SQLite Full Text Search (FTS) ist der Hammer.
Die Folien dazu.
Most blogposts I found on this topic don’t explain it from the beginning, so it took me quite a while to figure out how simple and powerful the sqlite fulltext search API (FTS3) actually is.
get the sqlite3 amalgamation sources (v3.6.22) and just unpack it into your iPhone project – sqlite3 as shipped on the …
Though CFArray comes with binary search capability, NSArray does not – at least not within the iPhone SDK. The indexOfObject:inSortedRange:options:usingComparator: can’t be found.
Plus the CFArrayBSearchValues doesn’t tell you whether the key actually is part of the list or not. That’s what the Java JDK does, so let’s implement some category methods
-(NSInteger)binarySearch:(id)key;
-(NSInteger)binarySearch:(id)key usingSelector:(SEL)comparator;
-(NSInteger)binarySearch:(id)key usingSelector:(SEL)comparator inRange:(NSRange)range;
-(NSInteger)binarySearch:(id)key …
The query optimiser for NSPredicate queries ontop CoreData/SQLite on the iPhone is a bit rudimentary (cough) and so I had to optimise myself to get binary-search enabled quick results:
+(NSPredicate*)findBySearchTerm:(NSString*)rawTerm within:(BOOL)within context:(NSManagedObjectContext*)context
{
NSSet *tokens = ;
if(tokens == nil || tokens.count < = 0)
…