Module which should (re)save a page field triggers an endless loop

[theoretic]

Hello everybody! And thanks for Processwire!

It appears that i have an interesting case concerning page fields resaving via modules. Let's suppose we're making a module which should run every time when a page is saved. Our module should calculate a value based on the values of some page fields, place this value to a dedicated field (in my case it's called 'mark') and save the page again. Below is the example of possible module code:

public function init() {
		$this->pages->addHookAfter('save', $this, 'hookCalculateMarks'); 
	}

private function calculateMarks($page) {
		$page->of(false);
		//doing some calculations...
		//$page->save(); //will trigger endless loop calling hookCalculateMarks again and again!
		$page->of(true);

		$this->message("Marks calculated.");
		$this->calculated = true;
		}

	public function hookCalculateMarks($event) {
		$page = $event->arguments[0];
		$this->calculateMarks($page);
	}

The problem is that the commented page->save() triggers a save event which triggers the hookCalculateMarks which triggers page->save() which triggers the hookCalculateMarks which... oops, my mysql server has gone away.

Tried to use a variable like $calculated...

	var $calculated = false;

	//some code skipped

	private function calculateMarks($page) {

		$page->of(false);
		//$page->save(); //will trigger endless loop calling hookCalculateMarks again and again!
		$page->of(true);

		$this->message("Marks calculated.");
		$this->calculated = true;
		}


	public function hookCalculateMarks($event) {
		$page = $event->arguments[0];
		if( $this->calculated ) return;
		$this->calculateMarks($page);
	}

 

...but the problem is still present. Endless loop again.

So what are the best practices for this case? What is the safe way to (re)save a field value afgter a page is saved?

Thanks in advance!

 

[OLSA]

Hello theoretic,

maybe you can try with add hook after "saveReady", and in that case also leave save part to PW api.
 

// pseudo example for your case
public function init() {
	$this->pages->addHookAfter('saveReady', $this, 'hookCalculateMarks'); 
}

public function hookCalculateMarks($event) {
	$page = $event->arguments[0];
	// if not desired template return
	if($page->template != 'your_template_name') return; 
	// eg. check if field marks is empty or 0
	if($page->marks < 1){		
		// some calculations... eg. using other page fields	
		$page->marks = $page->field_x + $page->field_y;		
	}	
}

As you can see there is no page "save" part.
This hook will check and set field value, and after it ProcessWire API will do the rest of the job.

Regards.

[psy]

Rather than saving the entire page when you're updating the 'mark' field, try 'setAndSave'. This will save only the nominated field and not trigger another page save event.

https://processwire.com/api/ref/page/set-and-save/

[netcarver]

9 hours ago, psy said:

Rather than saving the entire page when you're updating the 'mark' field, try 'setAndSave'. This will save only the nominated field and not trigger another page save event.

https://processwire.com/api/ref/page/set-and-save/

I use the method @psy is talking about and it works well.

[theoretic]

Thanks to all! Using  SaveReady is more logical in my case because i need the recalculation of my field (marks) just before the page will be saved. Works like a charm!

As to setAndSave, it will be more logical to use it in cases when there's no need to save the whole $page. However it's a very interesting approach also, thanks!