Thanks Robert. Docs PR is up: https://github.com/apache/beam/pull/13744
Brian On Tue, Jan 12, 2021 at 2:04 PM Robert Bradshaw <[email protected]> wrote: > Yes, a PTansform can have no sub-transforms, as long as it only returns > its inputs. Updating the docs would be a good idea. > > On Tue, Jan 12, 2021 at 1:04 PM Brian Hulette <[email protected]> wrote: > >> A recent bug with SqlTransform on Dataflow Runner V2 [1] revealed an >> interesting ambiguity in the Beam model: it's not clear if a composite >> transform is allowed to have zero sub-transforms [2]. This may sound like >> an academic concern, but it can happen if a PTransform returns its own >> input, making it a no-op. >> >> I tend to agree with Kenn's comment in the jira that we should allow it. >> If we don't this puts a burden on SDKs, they would need to either >> a) detect when a PTransform returns one of its inputs and raise an error, >> or >> b) find and replace any such no-ops before generating a portable pipeline >> graph >> >> If there aren't any objections to allowing "empty" composites I'll send a >> PR to clarify this in beam_runner_api.proto >> >> Brian >> >> [1] https://issues.apache.org/jira/browse/BEAM-11614 >> [2] >> https://github.com/apache/beam/blob/05c8471b27e03e5611a2a13137c4a785f2d17fc9/model/pipeline/src/main/proto/beam_runner_api.proto#L152-L155 >> >
