SilverStripe Subsite module delete all related data on subsite deletion - silverstripe

Question

I m using Silverstripe subsite module. When Subsite is deleted I want to delete all other information related to Subsite as well, like, Domains, Settings etc. I have created an extension that'll extend Subsite model.
<?php
class SubsiteExtension extends DataExtension {
public function onAfterWrite(){
parent::onAfterWrite();
//Some codes here
}
public function onBeforeDelete(){
//Check if member exist for Subsite, if so show warning.
}
public function onAfterDelete(){
$id = $this->owner->ID;
//DELETE ALL SUBDOMAINS RELATED TO DELETED SUBSITE
DB::query("DELETE FROM SubsiteDomain WHERE SubsiteID='".$id."'");
//DELETE SITE CONFIG
DB::query("DELETE FROM SiteConfig WHERE SubsiteID='".$id."'");
}
}
Problem
The code works flawlessly. Just wondering is there any other better way of deleting related records from other tables??
On method onBeforeDelete , how to show custom message saying "You can't delete this subsite unless you delete all the members" ?

Answer 1

Using onAfterDelete to delete related records is perfectly fine, although it really sounds a lot like you're doing unnecessary work here. Who's going to be bothered by some stray DB entries?
Regarding your onBeforeDelete approach: I would solve it otherwise. Override canDelete in your extension instead, something like this:
public function canDelete($member)
{
if( /* check if member exist for Subsite */ ){
return false;
}
// returning null here means that this extension doesn't influence
// the delete permission at this point
return null;
}
This will prevent deleting of the record in the CMS. Additionally, you could use updateCMSFields to display a notice to the user why he can't delete the record.
public function updateCMSFields(FieldList $fields)
{
if (!$this->owner->canDelete()) {
$fields->addFieldToTab(
'Root.Main',
LiteralField::create('_deleteInfo', 'Your info text')
);
}
}