Russell, My understanding is that onTrigger() will be called based on the scheduling of the processor, regardless of if there is an incoming flowfile. A couple of examples support this line of thought — “source” processors like GetFile, GenerateFlowFile, etc. run according to their schedule even though they will never receive a flowfile. Similarly, in ExecuteScript, the first task is always to attempt to retrieve a flowfile from the session and then yield execution if none is returned.
We may be able to add more explicit information to the Developer Guide, but I would suggest looking at Performing the Work [1] and When Processors Are Triggered [2] as they cover this topic. It seems in your case, your processor will either have no incoming connections, or you’ll need to add the @TriggerWhenEmpty annotation to your processor. [1] https://nifi.apache.org/docs/nifi-docs/html/developer-guide.html#performing-the-work <https://nifi.apache.org/docs/nifi-docs/html/developer-guide.html#performing-the-work> [2] https://nifi.apache.org/docs/nifi-docs/html/developer-guide.html#when-processors-are-triggered <https://nifi.apache.org/docs/nifi-docs/html/developer-guide.html#when-processors-are-triggered> Andy LoPresto [email protected] [email protected] PGP Fingerprint: 70EC B3E5 98A6 5A3F D3C4 BACE 3C6E F65B 2F7D EF69 > On Jun 8, 2017, at 3:45 PM, Russell Bateman <[email protected]> wrote: > > I'm doing something I've never done before in a custom processor. I'm writing > a processor that will awaken every /n/ minutes, query a database, perform > work as indicated by the result of the query, then go back to sleep for /n/ > minutes. > > This processor will never expect a flowfile because it doesn't work on > flowfile attributes or content. It may, I think, emit some flowfiles > downstream. > > Will onTrigger()be called without a flowfile? That point seems unclear in the > Developer Guide. Or is there some other lifecycle, like @OnScheduledthat I > should expect to use for this? > > Thanks, > > Russ
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