How to do SQL exception / error handling compatible with 2.5 and 3.x?

Question

I was trying to develop Joomla 2.5 and 3 component. As many things deprecated between these two versions and the way to throw and catch database and other errors, I could not find ways yet to make single component for both 2.5 and 3.

So is making component separately for 2.5 and 3.

Firstly, in 2.5 this way I am catching an error in database: -

if(!$database->query())
{ 
    return false; 
}

But how do I show or return exact error message to the view class so that error is displayed in the component?

Secondly, for another kind of db query, I am getting data from db this way in model class (here is my code in model's function):

$this->_data = null; 
if(JFactory::getApplication()->input->get('id') > 0) {
    $db = JFactory::getDBO();
    $db->setQuery("select * from `#__tablename_wrong` where `id`='".JFactory::getApplication()->input->get('id')."'");
}
if ($db->getErrorNum()) {
    JError::raiseWarning(500, $db->getErrorMsg());
}
$this->_data = $db->loadObject(); 
return $this->_data; 

Now I can inspect $this->_data in view class to see if 0 records return but again how do I display a specific database error message or return an error message to my view class to show errors?

So these are the most common ways developers should show errors while doing database queries in 2.5.

Answer 1

Pretty much the same as @ValentinDespa 's answer but i'm just gonna merge the two things together into something that will work in 2.5 and 3.x.

This rather than displaying a full page error message just returns false and then inserts an error message into the top of the page. Hope that's what you're after

$db = JFactory::getDbo();
$query = $db->getQuery(true);

$query->select('X') // This is specially added to throw an SQL error.
      ->from('#__users');
$db->setQuery($query);

if(!JError::$legacy)
{
    try
    {
        // If it fails, it will throw a RuntimeException
        $result = $db->loadResult(); 
    }
    catch (RuntimeException $e)
    {
        JFactory::getApplication()->enqueueMessage($e->getMessage());

        return false;
    }
}
else
{
    $result = $db->loadResult();

    // Check for a database error.
    if ($db->getErrorNum())
    {
        JFactory::getApplication()->enqueueMessage($db->getErrorMsg());

        return false;
    }
}

The JError legacy switch was false in 2.5 to use JError and then true in 3.x to use exceptions.

You can see a full example of me using this in one of my modules here https://github.com/JoomJunk/shoutbox/blob/development/mod_shoutbox/helper.php#L33

Answer 2

Watch out for exposing too much info! Please note that by throwing SQL errors into the wild, you may expose your database structure or other sensitive information. I would throw SQL errors only in backend (to let's say trusted users) and in frontend just a generic error and I would log the exact error in a error log.

Doing a query in 3.x catching and throwing exceptions

$db = JFactory::getDbo();
$query = $db->getQuery(true);

$query->select('X') // This is specially added to throw an SQL error.
      ->from('#__users');

try
{
    $db->setQuery($query);
    $result = $db->loadResult(); // If it fails, it will throw a RuntimeException 
}
catch (RuntimeException $e)
{
    throw new Exception($e->getMessage());
}

Doing a query in Joomla 2.5 and 3.x using old deprecated functions

$db = JFactory::getDbo();
$query = $db->getQuery(true);

$query->select('X'); // This is specially added to throw an SQL error.
      ->from('#__users');
$db->setQuery($query);

// Check for a database error.
if ($db->getErrorNum()) {
    JError::raiseWarning(500, $db->getErrorMsg());
}

$result = $db->loadResult();