DAG with a single operator

[Yogi Devendra]

Hi,

I am writing a Test application which does some validations on the HDFS
file.

Practically, I have single operator in my DAG which extends
AbstractFileInputOperator to do the necessary validation check.

public class OutputValidator extends AbstractFileInputOperator<String>

My output is just about writing log message saying SUCCESS or FAILURE
(which I can grep to find the status). I do not need any port, streams for
this operator.

Essentially, my DAG is just a single operator. Here is the code snippet for
populateDAG

 @Override
  public void populateDAG(DAG dag, Configuration conf)
  {
    dag.addOperator("OutputValidator", new OutputValidator());
  }

While launching this application; I am getting following error:

javax.validation.ValidationException: At least one output port must be
connected: OutputValidator
    at 
com.datatorrent.stram.plan.logical.LogicalPlan.validate(LogicalPlan.java:1720)
    at com.datatorrent.stram.StramClient.<init>(StramClient.java:140)
    at 
com.datatorrent.stram.client.StramAppLauncher.launchApp(StramAppLauncher.java:508)
    at com.datatorrent.stram.cli.DTCli$LaunchCommand.execute(DTCli.java:1928)
    at com.datatorrent.stram.cli.DTCli.launchAppPackage(DTCli.java:3382)
    at com.datatorrent.stram.cli.DTCli.access$7200(DTCli.java:109)
    at com.datatorrent.stram.cli.DTCli$LaunchCommand.execute(DTCli.java:1765)
    at com.datatorrent.stram.cli.DTCli$3.run(DTCli.java:1329)

Looks like, this is invalid DAG as per the platform definition.

Obviously, I can do some work around by adding some dummy port, stream.

But, my question is:
*Why should we call a DAG with a single operator as invalid*?

~ Yogi
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