Update component, where to retrieve the old version number from?

Question

I found by Joomla 3.x, that I can use an install script something like this:

class Com_ExampleInstallerScript
{
    public function install($adapter) 
    {
        // create tables
    }

    public function uninstall($adapter) 
    {
        // remove tables
    }

    public function update($adapter) 
    {
        // alter tables
    }

    public function preflight($route, $adapter) 
    {
        // stop service, probably creating a lock file
    }

    public function postflight($route, $adapter) 
    {
        // start service, probably removing a lock file
    }
}

Everything is fine except the update part. I guess this runs when I already have installed an older version and try to install the new version. If so, then how can I get the version number of the old version? I don't want to use upgrade SQL files, so that's not the answer.

Answer 1

You can get the old version like so:

class Com_ExampleInstallerScript
{
    protected $release = '';

    protected $paramTable = '#__modules';

    protected $extension = 'mod_mymodule';

    public function preflight($type, $parent)
    {
        // Module manifest file version
        $this->release = $parent->get('manifest')->version;

        // Abort if the module being installed is not newer than the currently installed version
        if (strtolower($type) == 'update')
        {
            $manifest   = $this->getItemArray('manifest_cache', '#__extensions', 'element', JFactory::getDbo()->quote($this->extension));
            $oldRelease = $manifest['version'];

            if (version_compare($this->release, $oldRelease, '<'))
            {
                JFactory::getApplication()->enqueueMessage(JText::sprintf('YOU_CANT_UPDATE_TO_A_LOWER_VERSION', $oldRelease, $this->release), 'error');
                return false;
            }
            if (version_compare($oldRelease, $this->release, '<'))
            {
                // If old version is the same as or less than 1.0.1
                if (version_compare($oldRelease, '1.0.1', '<='))
                {
                    // DO something here
                }
            }
        }
        return true;
    }
}

I've added a few comment to assist. Hope this helps