topic Re: multiInstanceLoopCharacteristics with an empty list in Alfresco Archive

multiInstanceLoopCharacteristics with an empty list

harry11 — Thu, 19 May 2011 15:31:17 GMT

Hello,I'm using a multiInstanceLoopCharacteristics with a List in my Activiti process. It works fine, except when the list is empty (the list is not null, it's just empty).When the list is empty I have this error :19 mai 2011 16:42:14 org.activiti.engine.impl.interceptor.CommandContext closeGRAVE: E

Re: multiInstanceLoopCharacteristics with an empty list

ronald_van_kuij — Fri, 20 May 2011 00:16:37 GMT

The error says it should be a positive integer. 0 not being that (nor a negative integer) And knowing Joram, I think it is implemented correctly. If you doubt this look at the specs. To prevent this, just add an exclusive gateway in front of it that does the 0 size check and bypasses this specific node.

Re: multiInstanceLoopCharacteristics with an empty list

harry11 — Fri, 20 May 2011 08:12:08 GMT

(Thank you for your answer, I fixed my problem this way, with gateways)

I can't find any information in the BPMN spec about the multiInstanceLoopCharacteristics semantic. I found in the Activiti user guide :

"A multi-instance activity is a way of defining repetition for a certain step in a business process. In programming concepts, a multi-instance matches the for each construct: it allows to execute a certain step or even a complete subprocess for each item in a given collection, sequentially or in parallel. "

For instance, in Java, when using the for each loop, the following code doesn't throw any exception :


List<String> list = new ArrayList<String>();
  for (String aString : list)
  {
   // doStuff
   assertEquals("Hello", aString);
  }

The loop is skipped.

Actually I think that "positive integer" usually refers to positives numbers + 0, and "strictly positive integer" doesn't include 0.

Re: multiInstanceLoopCharacteristics with an empty list

ronald_van_kuij — Fri, 20 May 2011 12:54:17 GMT

Actually I think that "positive integer" usualy refers to positives numbers + 0, and "strictly positive integer" doesn't include 0.

Not in xsd's 🙂 and java is java (not bpmn or xml).

But… I did scan the spec to and there is indeed no reference that it might not be a size of 0 and what the behaviour should be then. I might have missed something though… question for the experts…

Re: multiInstanceLoopCharacteristics with an empty list

frederikherema1 — Fri, 20 May 2011 13:46:09 GMT

What is exactly the issue? It doesn't make sense to have an multi-activity be have zero instances executed (messes up the flow history as well)

Re: multiInstanceLoopCharacteristics with an empty list

harry11 — Fri, 20 May 2011 14:01:18 GMT

What is exactly the issue? It doesn't make sense to have an multi-activity be have zero instances executed (messes up the flow history as well)

Well, sometimes, in my case, I need to have 0 instance executed.

No instance -> the loop is skipped.
That's the way the for each loop usually works, isn't it ?

Re: multiInstanceLoopCharacteristics with an empty list

frederikherema1 — Fri, 20 May 2011 14:11:49 GMT

That's how it works in porgramming, true But the foreach was just mentioned in userguide to make analogy with the concept of looping over each item…

Only workaround I can think of is modeling a exclusive gateway around the MI-activity which checks the list's size for 0…

Re: multiInstanceLoopCharacteristics with an empty list

harry11 — Fri, 20 May 2011 14:17:01 GMT

Right, the exclusive gateway trick is the solution I use.

I let this topic open since I think it needs to be checked, then added in the Activiti User Guide.

Thanks every one for your help 😉

Re: multiInstanceLoopCharacteristics with an empty list

ronald_van_kuij — Fri, 20 May 2011 15:07:46 GMT

What is exactly the issue? It doesn't make sense to have an multi-activity be have zero instances executed (messes up the flow history as well)

Why does it mess up the flow history? Because Activiti implements this in a specific way (it is Activiti specific anyway) ? That should be the argument. With multi instances there is an inner and outer part. The outer part could still be 'executed' e.g. So no problem with the history flow then.

But these are implementation issues. I'm more curious to whether it is allowd according to the spec to have a size of zero. I read about a default of 1 if you do not want it base on the size of something you pass in and do not provide an explicit number. Further more the explicit number you can provide must be an xsd:integer, so even a -1 could be provided… A size of -1 is difficult, but a size of 0 not… So… food for thought

Re: multiInstanceLoopCharacteristics with an empty list

frederikherema1 — Mon, 23 May 2011 09:49:00 GMT

Ronald, you're right, it won't mess up history since there have inner and outer executions (my bad) Spec doesn't seem to mention any limititations on the number of items in the collection…

Re: multiInstanceLoopCharacteristics with an empty list

ronald_van_kuij — Mon, 23 May 2011 11:06:43 GMT

(my bad)

You can't know everything, believe me…… I've tried…. for several hundered years now…

Re: multiInstanceLoopCharacteristics with an empty list

frederikherema1 — Wed, 25 May 2011 08:02:23 GMT

You can't know everything, believe me…… I've tried…. for several hundered years now…

ROFL

Re: multiInstanceLoopCharacteristics with an empty list

p4w3l — Fri, 17 May 2013 11:42:38 GMT

It is annoying having extra gateway to test collection emptiness. If you see no reason to restrict empty collections maybe they could be allowed?

Re: multiInstanceLoopCharacteristics with an empty list

melentye — Sat, 18 May 2013 08:37:59 GMT

I second that, if it doesn't violate the BPMN2 spec or any other standards, it would be more convenient to skip for-each loops on empty collections without using an additional gateway

Re: multiInstanceLoopCharacteristics with an empty list

ronald_van_kuij — Sun, 19 May 2013 09:44:01 GMT

Fastest way to get this fixed is to fork the code on github, createva patch, add a testcase and make sure all other tests still run fine. Then createva pull request et voila…

Re: multiInstanceLoopCharacteristics with an empty list

dromie — Tue, 09 Sep 2014 11:41:58 GMT

Hi,

I ran into the same situation, and I've made the modification as well.
Here you go: https://github.com/Activiti/Activiti/pull/364
Should I also raise a Jira ticket for this?

Cheers,
dromie

Re: multiInstanceLoopCharacteristics with an empty list

guillaume1 — Mon, 22 Jun 2015 12:19:49 GMT

Hi,

What is the status of this request ?
Is it already included in latest version of Activiti ? Is it planned to include it ?

We have a lots of cases where the multi instance collection is generated dynamically and empty lists are a valid result from the service point of view.

Cheers,
Guillaume.

Re: multiInstanceLoopCharacteristics with an empty list

martin_grofcik — Tue, 23 Jun 2015 06:22:00 GMT

Hi,

yes it is supported since September 2014. e.g org.activiti.engine.test.bpmn.multiinstance.MultiInstanceTest#testSequentialEmptyCollection
Regards
Martin