PHP/Propel delete record 1:n - php

Question

I've got two tables: step and links joined 1:n. I'm aiming to maintain the links through the step objects. I retrieve all steps from the database and populate the relation with the links table. I persist the step object containing a collection of links to JSON and return it to the front end using REST.
That means that if a step is linked or unlinked to another step in the front end I send the entire step back to the backend including a collection of links. In the back end I use the following code:
public function put($processStep) {
if (isset($processStep['Processesid']) && isset($processStep['Coordx']) && isset($processStep['Coordy'])) {
$p = $this->query->findPK($processStep['Id']);
$p->setId($processStep['Id']);
$p->setProcessesid($processStep['Processesid']);
if (isset($processStep['Flowid'])) $p->setFlowid($processStep['Flowid']);
if (isset($processStep['Applicationid'])) $p->setApplicationid($processStep['Applicationid']);
$p->setCoordx($processStep['Coordx']);
$p->setCoordy($processStep['Coordy']);
$links = $p->getLinksRelatedByFromstep();
$links->clear();
foreach ($processStep['Links'] as $link) {
if (!isset($link['Linkid'])) {
$newLink = new \Link();
$newLink->setFromstep($link['Fromstep']);
$newLink->setTostep($link['Tostep']);
$links->prepend($newLink);
}
}
$p->save();
return $p;
} else {
throw new Exceptions\ProcessStepException("Missing mandatory fields.", 1);
}
}
I'm basically deleting every link from a step and based upon the request object I recreate the links. This saves me the effort to compare what links are deleted and added. The insert work like a charm Propel automatically creates the new links. Thing is it doesn't delete like it inserts. I've checked the object that is being persisted ($p) and I see the link being deleted but in the MySQL log there is absolutely no action being performed by Propel. It looks like a missing member from the link collection doesn't trigger a dirty flag or something like that.
Maybe I'm going about this the wrong way, I hope someone can offer some advice.
Thanks

Answer 1

To delete records, you absolutely always have to use delete. The diff method on the collection is extremely helpful when determining which entities need added, updated, and deleted.

Answer 2

Thanks to Ben I got on the right track, an explicit call for a delete is not needed. I came across a function called: setRelatedBy(ObjectCollection o) I use this function to provide a list of related objects, new objects are interpreted as inserts and omissions are interpreted as deletes.
I didn't find any relevant documentation regarding the problem so here's my code:
$p = $this->query->findPK($processStep['Id']);
$p->setId($processStep['Id']);
$p->setProcessesid($processStep['Processesid']);
$p->setCoordx($processStep['Coordx']);
$p->setCoordy($processStep['Coordy']);
if (isset($processStep['Flowid'])) $p->setFlowid($processStep['Flowid']);
if (isset($processStep['Applicationid'])) $p->setApplicationid($processStep['Applicationid']);
//Get related records, same as populaterelation
$currentLinks = $p->getLinksRelatedByFromstep();
$links = new \Propel\Runtime\Collection\ObjectCollection();
//Check for still existing links add to new collection if so.
//This is because creating a new Link instance and setting columns marks the object as dirty creating an exception due to duplicate keys
foreach ($currentLinks as $currentLink) {
foreach ($processStep['Links'] as $link) {
if (isset($link['Linkid']) && $currentLink->getLinkid() == $link['Linkid']) {
$links->prepend($currentLink);
break;
}
}
}
//Add new link objects
foreach ($processStep['Links'] as $link) {
if (!isset($link['Linkid'])) {
$newLink = new \Link();
$newLink->setFromstep($link['Fromstep']);
$newLink->setTostep($link['Tostep']);
$links->prepend($newLink);
}
}
//Replace the collection and save the processstep.
$p->setLinksRelatedByFromstep($links);
$p->save();