Friday, June 19, 2009

The problem with flags in Metastorm BPM

Flags are a great way to pass data between processes or to pass data from an external application to Metastorm BPM. There are several ways to raise flags, via the eRaiseFlag executable, using the Raise Flag ActiveX control, via the engine’s XML interface or through the engine’s COM interface. FreeFlow provides a wrapper around the last two approaches. Usage is pretty simple

      Connection conn = new Connection();
      // use to switch between TP and COM
      conn.RaiseFlagBy = RaiseFlagBy.TransactionProtocol;
      conn.RaiseFlag("New Data", new string[] {"some data", "1"});

As an aside, eagle eyed C# coders may be wondering why the last parameter of RaiseFlag doesn’t use the params keyword to simplify usage even further. The problem is there are several overloads of this method (taking user name, password, folder ID etc) so adding params would confuse the compiler since there would be multiple matches for a call to RaiseFlag. One solution would be to give the method a different name but this would make the API less discoverable since different versions of the same method would have different names. Another solution would be to just have one version of the method, with all the required parameters, but that wouldn’t really make life any simpler since the simple usage above would require passing in all parameters. API design isn’t an exact science and sometimes compromises are required.

But back to the main point of this post. Say we are going to create a new folder in Metastorm BPM using the flag data passed to populate the custom variables. Typically this might happen when somebody fills in an online ASP.NET form and we want to kick off some kind of process in Metastorm based on that data. So we’ll have a flagged creation action in the process and add some code to read the data, like so.


Which works fine. OK, say we change the data passed in to

conn.RaiseFlag("New Data", new string[] {"some\tdata", "1"});

Now when we run the code we don’t get a folder created. Instead we get an error in the Designer Log saying “'%inumber' failed while evaluating expression '%iNumber:=data' Error setting value for custom folder field 'inumber'”. This is because flag data passed to the engine is tab-delimited, so if your actual data contains tabs, everything gets screwed up.

We have two problems to solve here. First, how do we handle data with tabs in it, since we probably can’t stop tabs being entered by the user of the ASP.NET form. Secondly, how do we deal with any kind of failure to parse the data passed. This is more of a problem, since currently if we fail to parse the data, we lose it all since the folder never gets created.

robust flagsSo tackling the second problem first, we want to do as little work as possible in the flagged creation action. We will just assign the flag data to a temporary memo variable, since the flag data will not be available outside the flagged action.


You may find this won’t work for you in earlier versions, at some point only each individual item of flag data could be accessed but it looks to have been fixed in version 7.6. If it doesn’t work, you’ll need to manually combine each piece of flag data.

Next in the Parse conditional action (with no condition), we attempt to assign the flag data to the variables, like so


This will still fail and will stay at the ‘Got Data’ stage, but at least we haven’t lost the data. The Edit action can then be used to manually fix up the data and get the folder on its way.

So back to the first problem, handling tabs in flag data. Really the only solution to this is to use a different delimiter when raising the flag. None of them are perfect, since potentially any of them could be in the data, but %CHR(160) has worked well for us in the past. Another solution might be to pass your data in some other format such as XML. That will be more complicated but more robust. 

No comments: