Lesson 5: Deleting data from the database

The application is now able to display names from the database, and the user is able to add new names using a custom view. It is not yet possible for the user to remove a name. This lesson adds the deletion functionality using the swipe-to-delete functionality available in many iPhone applications.

Deleting the name from the database

To delete the name from the database, use the same SQL statement as the select, but open the result set for update so that you can delete the selected row. Add the following method to the DataAccess class:

- (void)removeNameAtIndexPath:(NSIndexPath *)indexPath {
    // +1 to the index since the DB uses a 1-based index rather than 0-based
    ULPreparedStatement *prepStmt = 
     connection->PrepareStatement(
      [[NSString stringWithFormat:SELECT_STMT, indexPath.row + 1] UTF8String]);
    
    if (prepStmt) {
        ULResultSet        *resultSet = prepStmt->ExecuteQuery();
        
        resultSet->First();
        resultSet->Delete();
        resultSet->Close();
        prepStmt->Close();
        connection->Commit(); // Commit the deletion.
    } else { 
        NSLog(@"Couldn't prepare SELECT with index for delete.");
    }
}

Also add the method signature to the header.

Enabling the swipe-to-delete

In order to enable the delete functionality, simply copy the comment template of the tableView:commitEditingStyle:forRowAtIndexPath method from RootViewController into the DataAccess class and call the removeNameAtIndexPath method you just created.

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source.
        [[DataAccess sharedInstance] removeNameAtIndexPath:indexPath];
        [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] 
                         withRowAnimation:UITableViewRowAnimationFade];
    } else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
    } 
}

The application is now complete. The table view displays the list of names in alphabetical order, new names can be added using the NewNameViewController and names can be removed using the familiar swipe-to-delete gesture.

Discuss this page in DocCommentXchange.