Question

I have an app which pretty much follows the method described here. The key code is as follows:

#import <Foundation/Foundation.h>
#import <sqlite3.h>     
@interface FailedBankDatabase : NSObject {
    sqlite3 *_database;
}     
+ (FailedBankDatabase*)database;
- (NSArray *)failedBankInfos;    
@end

#import "FailedBankDatabase.h"
#import "FailedBankInfo.h"
@implementation FailedBankDatabase
static FailedBankDatabase *_database;

+ (FailedBankDatabase*)database {
if (_database == nil) {
    _database = [[FailedBankDatabase alloc] init];
}
return _database;
}

- (id)init {
if ((self = [super init])) {
    NSString *sqLiteDb = [[NSBundle mainBundle] pathForResource:@"banklist" 
        ofType:@"sqlite3"];

    if (sqlite3_open([sqLiteDb UTF8String], &_database) != SQLITE_OK) {
        NSLog(@"Failed to open database!");
    }
}
return self;
}

- (void)dealloc {
    sqlite3_close(_database);
    [super dealloc];
}

Now, the app works with one database as expected. But, I want to be able to switch to a different database when the user touches a button. I have the button handler and logic OK, and I store the name of the database to be used and can retrieve it. But, no matter what I do, I always get the same (original) database being called. I fear that the handle associated with _database, a object of type sqlite3, in the example is not being changed properly, so I don’t open the database properly. How should I go about changing this? You can’t re-init a singleton, but I need to change what’s stored in it, in this case _database. Thanks.

EDIT: I would add that if I ask for _database is a pointer. So I need to open a new database (and close the first I guess) and give the new database a new address in the process.

Answer 1

I had the same problem, but couldn’t modify the database (they were used in other projects).

So, I created a method called useDatabase:, that close the previous connection, and open a new one.

The steps :
Your – (id)init remains the same

In FailedBankDatabase, you create a method that close and open the database with the name of the new database

-(void)useDatabase:(NSString*)database {

    sqlite3_close(_database);

    NSString *sqLiteDb = [[NSBundle mainBundle] pathForResource:database 
    ofType:@"sqlite3"];

    if (sqlite3_open([sqLiteDb UTF8String], &_database) != SQLITE_OK) {
        NSLog(@"Failed to open database!");
    }

}

At the very beggining (for example in appDidFinishLaunching), you call the singleton once

[FailedBankDatabase database];

, so that it is first initialised.

Then, when you want to change the .sqlite used, you can call :

[FailedBankDatabase useDatabase:@”anOtherDatabase”]

I think you can do this when you don’t have to change the database very often. In my case, I use this once at the very first screen, with 3 buttons, where I will choose wich database will be used.

For more complicated cases, for exemple involving multithreading, you should not do that since it closes the connection for a little time, while it is used elsewhere.

Hope it helps,

Jery