How to deal with accented characters in iOS SQLite?

Question

I need to perform a SELECT queries that are insensitive to case and accents. For demo purposes, I create a table like that:

create table table
(
  column tex         


        

Answer 1

Two basic approaches:

1. You can create a second column in the table which contains the string without the international characters. Furthermore, before doing a search against this secondary search column, you should also remove international characters from the string being search for, too (that way you are comparing non-international to non-international).

   This is the routine I use to convert the international characters:

   NSData *data = [string dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
   string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
   

   You could also replace the accented characters with:

   NSMutableString *mutableString = [string mutableCopy];
   CFStringTransform((__bridge CFMutableStringRef)mutableString, NULL, kCFStringTransformStripCombiningMarks, NO);
   

   By the way, if you need to sort your results, you can also sort upon this secondary search field instead of the main field, which will avoid problems stemming from SQLite's inability to sort the international characters, either.

2. You can alternatively create your own "unaccented" C function (define this C function outside the @implementation for your class):

   void unaccented(sqlite3_context *context, int argc, sqlite3_value **argv)
   {
       if (argc != 1 || sqlite3_value_type(argv[0]) != SQLITE_TEXT) {
           sqlite3_result_null(context);
           return;
       }
   
       @autoreleasepool {
           NSMutableString *string = [NSMutableString stringWithUTF8String:(const char *)sqlite3_value_text(argv[0])];
           CFStringTransform((__bridge CFMutableStringRef)string, NULL, kCFStringTransformStripCombiningMarks, NO);
           sqlite3_result_text(context, [string UTF8String], -1, SQLITE_TRANSIENT);
       }
   }
   

   You can then define a SQLite function that will call this C-function (call this method after you open the database, which will be effective until you close that database):

   - (void)createUnaccentedFunction
   {
       if (sqlite3_create_function_v2(database, "unaccented", 1, SQLITE_ANY, NULL, &unaccented, NULL, NULL, NULL) != SQLITE_OK)
           NSLog(@"%s: sqlite3_create_function_v2 error: %s", __FUNCTION__, sqlite3_errmsg(database));
   }
   

   Having done that, you can now use this new unaccented function in SQL, e.g.:

   if (sqlite3_prepare_v2(database, "select a from table where unaccented(column) like 'a'", -1, &statement, NULL) != SQLITE_OK)
       NSLog(@"%s: insert 1: %s", __FUNCTION__, sqlite3_errmsg(database));