Creating a singleton DB helper class - ios

Question

I am trying to write a Master-Detail application that gets it's data from a sqlite database. As part of this I'm trying to create a helper class that creates a singleton instance of my database. All I want it to do is initialise the database so I can then reference this from the different views of the application.
I followed a tutorial that does this here: http://www.raywenderlich.com/913/sqlite-101-for-iphone-developers-making-our-app
I got the tutorial to work however now I am trying to modify it to fit my application and I can't seem to get it working. I have no errors or warnings but when I run the app on the emulator none of the debug text I have put in executes. So it looks to me like my init function is not executing. I just can't figure out why.
Can anyone spot my problem in the code below?
LoyaltyProgramDatabase.h
#import <Foundation/Foundation.h>
#import <sqlite3.h>
#interface LoyaltyProgramDatabase : NSObject {
sqlite3 *_loyaltyProgDB;
}
#property (strong, nonatomic) NSString *databasePath; //Path file of our database
#property (nonatomic) sqlite3 *loyaltyProgDB; //Reference to the database
+ (LoyaltyProgramDatabase*)loyaltyProgDB;
#end
LoyaltyProgramDatabase.m
#import "LoyaltyProgramDatabase.h"
#implementation LoyaltyProgramDatabase
static LoyaltyProgramDatabase *_loyaltyProgDB;
//Create a singleton instance of loyaltyProgDB
+ (LoyaltyProgramDatabase*)loyaltyProgDB {
if (_loyaltyProgDB == nil) {
_loyaltyProgDB = [[LoyaltyProgramDatabase alloc] init];
}
return _loyaltyProgDB;
}
- (id)init {
NSLog(#"Inside init function");
if ((self = [super init])) {
NSString *docsDir;
NSArray *dirPaths;
// Get the documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = dirPaths[0];
// Build the path to the database file
_databasePath = [[NSString alloc] initWithString: [docsDir stringByAppendingPathComponent:#"loyaltyProg.db"]];
NSFileManager *filemgr = [NSFileManager defaultManager];
if ([filemgr fileExistsAtPath: _databasePath ] == NO)
{
const char *dbpath = [_databasePath UTF8String];
if (sqlite3_open(dbpath, &_loyaltyProgDB) == SQLITE_OK)
{
char *errMsg;
const char *sql_stmt = "CREATE TABLE IF NOT EXISTS scoreCard (ID INTEGER PRIMARY KEY AUTOINCREMENT, campaignID INTEGER, merchantName TEXT)";
if (sqlite3_exec(_loyaltyProgDB, sql_stmt, NULL, NULL, &errMsg) != SQLITE_OK)
{
//_status.text = #"Failed to create table";
NSLog(#"Failed to create table");
}
sqlite3_close(_loyaltyProgDB);
} else {
//_status.text = #"Failed to open/create database";
NSLog(#"Failed to open/create database");
}
}
}
return self;
}
- (void)dealloc {
sqlite3_close(_loyaltyProgDB);
}
#end

Answer 1

Try this:
+ (id)allocWithZone:(NSZone *)zone
{
return [self loyaltyProgDB];
}
+ (LoyaltyProgramDatabase*)loyaltyProgDB
{
static BNRImageStore *loyaltyProgDB = nil;
if (!loyaltyProgDB) {
// Create the singleton
loyaltyProgDB = [[super allocWithZone:NULL] init];
}
return loyaltyProgDB;
}
- (id)init {
self = [super init];
if (self) {
NSString *docsDir;
NSArray *dirPaths;
// Get the documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = dirPaths[0];
// Build the path to the database file
_databasePath = [[NSString alloc] initWithString: [docsDir stringByAppendingPathComponent:#"loyaltyProg.db"]];
NSFileManager *filemgr = [NSFileManager defaultManager];
if ([filemgr fileExistsAtPath: _databasePath ] == NO)
{
const char *dbpath = [_databasePath UTF8String];
if (sqlite3_open(dbpath, &_loyaltyProgDB) == SQLITE_OK)
{
char *errMsg;
const char *sql_stmt = "CREATE TABLE IF NOT EXISTS scoreCard (ID INTEGER PRIMARY KEY AUTOINCREMENT, campaignID INTEGER, merchantName TEXT)";
if (sqlite3_exec(_loyaltyProgDB, sql_stmt, NULL, NULL, &errMsg) != SQLITE_OK)
{
//_status.text = #"Failed to create table";
NSLog(#"Failed to create table");
}
sqlite3_close(_loyaltyProgDB);
} else {
//_status.text = #"Failed to open/create database";
NSLog(#"Failed to open/create database");
}
}
}
return self;
}

Answer 2

If you have not written a line of code that says [[LoyaltyProgramDatabase alloc] init] or [LoyaltyProgramDatabase loyaltyProgDB], then your init function is never getting called.
The init is not automatically called when you start the app. The only time any init function is called automatically is if you have a UI element in a nib/xib/storyboard file, and the app creates the element utilizing various initialization functions, but never your own init function. But for something like what you have written, to initialize the database object, you need to call the init function yourself.
In your app delegate, under the didFinishLaunching function, put this line:
[LoyaltyProgramDatabase loyaltyProgDB];
This isn't a really up-to-date singleton pattern by the way. This is actually a lazy loader function. If you want a more secure singleton, use this code.
+(id)sharedInstance {
static dispatch_once_t pred = 0;
__strong static id _sharedObject = nil;
dispatch_once(&pred, ^{
_sharedObject = [[self alloc] init];
});
return _sharedObject;
}
This will make sure the database is only ever initialized once and it is thread safe. To create/use the singleton, the code would change from the above to
[LoyaltyProgramDatabase sharedInstance]