Error when streaming and using flow variables (constant value column, string manipulation, and rule engine)

Hello KNIME Community,

I am getting errors when I try to stream using any of these three nodes: constant value column, string manipulation, and rule engine and use a flow variable to try and have them replace a column with a constant value. The same error occurs when appending a new column. I have made sure that the flow variable I am referencing is included in the component input but you will see for the string manipulation it is even giving me an error saying that flow variable doesn’t exist. The other two nodes are saying that their configuration failed. This problem only occurs when streaming when I turn off streaming everything runs as expected.

I am still using KNIME version 4.3.4 because that is what our server supports right now. Any alternatives or clarifications that anyone can give me regarding why this is happening and if/how I could fix it would be much appreciated! I have attached an example workflow for reference.

Thank you in advance for the help!

failing_flow_variable_streaming.knwf (29.0 KB)

I can confirm that this doesn’t work on KNIME AP 4.5.2 as well. (I used a Table Creator instead of the Random Number Generator because I don’t have that extension).

The error message in the console suggests that the Component Input doesn’t get executed, resulting in absent Flow Variables.

1 Like

Just wanted to keep this topic alive since there hasn’t been any updates

Hi @Kaegan -

Good catch on this one, it definitely seems to be a bug. Coincidentally someone else stumbled across this independently just last week from our side. At any rate there is a ticket now (AP-19128) - we’ll update in this thread when there is progress to report.

Sorry for the delayed response, and thank you for providing a workflow that easily reproduces the problem :+1:


Hey @ScottF

Thank you for responding!! For anyone else needing a workaround to the same problem of needing a constant value column created using a flow variable in a streaming component I was able to successfully use a variable to table row node and a cross joiner to accomplish this. Not ideal but it works and doesn’t make it significantly slower!!

I’ll leave the topic open for now until there is an update in the future, thank you again!


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