text: #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 ) 
      {
          DLog(@"Database is not an in-memory representation." );
          return NO;
      }
      
      // and only if the database is open
      if ( self->_db == nil ) 
      {
          DLog(@"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 )
      {
          DLog(@"Database is not an in-memory representation." );
          return NO;
      }
      
      // and only if the database is open
      if ( self->_db == nil ) 
      {
          DLog(@"Invalid database connection." );
          return NO;
      }
      
      // save the in-memory representation    
      return ( SQLITE_OK == loadOrSaveDb( self->_db, [filePath fileSystemRepresentation], true ) );
  }
  
  @end
  