Optional Input Nodes

[beetleskin]

Hi, I got the use-case of an aggregation node that accumulates data from nodes of a certain type. Specifically: I got several nodes producing GeoJson data. Now I want to accumulate those with a Section or Widget. For the section, at least one GeoJson is required, but in general the inputs are optional. I just want to render what's available from the bag, i.e. sometimes some topics are missing and one or another GeoJson node fails. I wonder how to model this situation correctly with Marv:

Either I collect all nodes of a certain type, e.g.:

@marv.node(Section)
@marv.input('geojson_streams', default=[magically collect all GeoJson nodes])
def my_trajectory_section(geojson_streams):
  geojson_streams = marv.pull_all(*geojson_streams)
  if not any(all_geojson_streams):
    # no valid input, nothing to do
    raise marv.Abort()
  for s in geojson_streams:
    geojson = marv.pull(s)
    if geojson is not None:
      # do something with valid s

or I list all nodes explicitly:

@marv.node(Section)
@marv.input('geojson_stream_a', default=geojson_node_a)
@marv.input('geojson_stream_b', default=geojson_node_b)
...
@marv.input('geojson_stream_n', default=geojson_node_n)
def my_trajectory_section(geojson_streams_a, geojson_stream_b):
  geojson_streams = marv.pull_all(geojson_streams_a, geojson_streams_b)
  if not any(geojson_streams):
    # no valid input, nothing to do
    raise marv.Abort()
  for s in geojson_streams:
    geojson = marv.pull(s)
    if geojson is not None:
      # do something with valid s

The first solution does not exist afaik. The second solution fails, since the my_trajectory_section fails resp. is not executed, if any of its inputs are missing.

[chaoflow]

@beetleskin For the moment, the best solution seems to be the second one in combination with using bagmeta as an input and to pull the other inputs depending on which topics are listed on bagmeta, i.e. available. What do you think?

[beetleskin]

Sounds like a workaround, but how would I do that? How would I pull streams within a node depending on some condition (e.g. whether a topic is available in bagmeta), I thought one needs to declare that with the @marv.input(..) decorator ..?

[chaoflow]

@beetleskin you would declare all that you know can exist, but pull only those that you know exists (from reading bagmeta).

Do your geojson nodes differ in code or do they only consume different topics?

[chaoflow]

@beetleskin Your first initially described solution is tracked as feature request in https://github.com/ternaris/marv-robotics/issues/38 and optional inputs are now supported. See https://ternaris.com/marv-robotics/docs/patterns.html#optional-inputs.