R – Windows workflow – Cannot handle exception in ReceiveActivity

exception handlingworkflow-foundation

I have a sequential workflow, which is hosted in IIS as a Workflow Service.

My workflow starts with a ReceiveActivity, and inside the ReceiveActivity a call is made to a WCF service with a SendActivity. If this call receives an exception, there is a FaultHandlerActivity on my ReceiveActivity which is meant to handle the call, and send a default value back to the client.

What is happening in my client is that an exception on the SendActivity is bubbling back to the client as a FaultException, even though my FaultHandlerActivity is running (I verified this by logging the beginning and end of the single CodeActivity in my fault handler)

My question is: How can I swallow exceptions ocurring in the SendActivity, without a FaultException being returned to the client?

Best Answer

OK, I figured it out.

My receiveActivity had a fault handler directly on it. What happens then is that if any child activity raises an exception, the fault handler on the receive activity is invoked, and it is also set to a Faulted state, and the exception received is returned to the client application - whether I wanted that or not.

The solution was to add a sequence activity inside the receiveActivity, do all of the processing inside the sequence activity, and add a faultHandlerActivity to the Sequence, which sets up my default return value.

The receive activity is never faulted, and the exception is not returned to my client, but the default value set up in the Sequence's FaultHandler is returned.

Hopefully this will help someone else with the same issue

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Python – How to test that a Python function throws an exception

Use TestCase.assertRaises (or TestCase.failUnlessRaises) from the unittest module, for example:

import mymod

class MyTestCase(unittest.TestCase):
    def test1(self):
        self.assertRaises(SomeCoolException, mymod.myfunc)

Python – How to write a `try`/`except` block that catches all exceptions

Apart from a bare except: clause (which as others have said you shouldn't use), you can simply catch Exception:

import traceback
import logging

try:
    whatever()
except Exception as e:
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    # Logs the error appropriately.

You would normally only ever consider doing this at the outermost level of your code if for example you wanted to handle any otherwise uncaught exceptions before terminating.

The advantage of except Exception over the bare except is that there are a few exceptions that it wont catch, most obviously KeyboardInterrupt and SystemExit: if you caught and swallowed those then you could make it hard for anyone to exit your script.

Best Answer

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Python – How to test that a Python function throws an exception

Python – How to write a `try`/`except` block that catches all exceptions

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