feeling/FMDB2_1/extra/FMDatabase+InMemoryOnDiskIO.m

#import "FMDatabase+InMemoryOnDiskIO.h"

// http://www.sqlite.org/backup.html
static
int loadOrSaveDb(sqlite3 *pInMemory, const char *zFilename, int isSave)
{
    int rc;                   /* Function return code */
    sqlite3 *pFile;           /* Database connection opened on zFilename */
    sqlite3_backup *pBackup;  /* Backup object used to copy data */
    sqlite3 *pTo;             /* Database to copy to (pFile or pInMemory) */
    sqlite3 *pFrom;           /* Database to copy from (pFile or pInMemory) */
    
    /* Open the database file identified by zFilename. Exit early if this fails
     ** for any reason. */
    rc = sqlite3_open(zFilename, &pFile);
    if( rc==SQLITE_OK ){
        
        /* If this is a 'load' operation (isSave==0), then data is copied
         ** from the database file just opened to database pInMemory. 
         ** Otherwise, if this is a 'save' operation (isSave==1), then data
         ** is copied from pInMemory to pFile.  Set the variables pFrom and
         ** pTo accordingly. */
        pFrom = (isSave ? pInMemory : pFile);
        pTo   = (isSave ? pFile     : pInMemory);
        
        /* Set up the backup procedure to copy from the "main" database of 
         ** connection pFile to the main database of connection pInMemory.
         ** If something goes wrong, pBackup will be set to NULL and an error
         ** code and  message left in connection pTo.
         **
         ** If the backup object is successfully created, call backup_step()
         ** to copy data from pFile to pInMemory. Then call backup_finish()
         ** to release resources associated with the pBackup object.  If an
         ** error occurred, then  an error code and message will be left in
         ** connection pTo. If no error occurred, then the error code belonging
         ** to pTo is set to SQLITE_OK.
         */
        pBackup = sqlite3_backup_init(pTo, "main", pFrom, "main");
        if( pBackup ){
            (void)sqlite3_backup_step(pBackup, -1);
            (void)sqlite3_backup_finish(pBackup);
        }
        rc = sqlite3_errcode(pTo);
    }
    
    /* Close the database connection opened on database file zFilename
     ** and return the result of this function. */
    (void)sqlite3_close(pFile);
    return rc;
}



@implementation FMDatabase (InMemoryOnDiskIO)

- (BOOL)readFromFile:(NSString*)filePath
{
    // only attempt to load an on-disk representation for an in-memory database
    if ( self->_databasePath != nil ) 
    {
        NSLog(@"Database is not an in-memory representation." );
        return NO;
    }
    
    // and only if the database is open
    if ( self->_db == nil ) 
    {
        NSLog(@"Invalid database connection." );
        return NO;
    }
    
    return ( SQLITE_OK == loadOrSaveDb( self->_db, [filePath fileSystemRepresentation], false ) );

}

- (BOOL)writeToFile:(NSString *)filePath
{
    // only attempt to save an on-disk representation for an in-memory database
    if ( self->_databasePath != nil )
    {
        NSLog(@"Database is not an in-memory representation." );
        return NO;
    }
    
    // and only if the database is open
    if ( self->_db == nil ) 
    {
        NSLog(@"Invalid database connection." );
        return NO;
    }
    
    // save the in-memory representation    
    return ( SQLITE_OK == loadOrSaveDb( self->_db, [filePath fileSystemRepresentation], true ) );
}

@end