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Subject: Re: "Invalid request" for simply "pvget ThePV" when all other requests seem fine
From: "Kasemir, Kay" <[email protected]>
To: Andrew Johnson <[email protected]>, "[email protected]" <[email protected]>
Date: Tue, 28 Aug 2018 18:09:03 +0000
Hi Andrew:

> .. "field(value)" seems to have always been the default...
> What does your older pvget show for its help text?

Same as the new one:

  -r <pv request>:   Request, specifies what fields to return and options, default is 'field(value)'

> this change in behavior looks like a regression now that you point it out.

Yes, it is a change. In the old code, I find this in EPICS-CPP-4.6.0/pvAccessCPP/pvtoolsSrc/pvget.cpp:

               // probe for value field
...
                        if (structure.get() == 0 || structure->getField("value").get() == 0)
                        {
                            // fallback to structure
                            mode = StructureMode;
                            pvRequest = CreateRequest::create()->createRequest("field()");
                        }

That must be what made it tolerant to a missing "value" field, falling back to getting everything.

The new pvget code doesn't update the pvRequest. In the printout section, it's prepared to say "no value field" if there is none, but then it's already too late, because it forced the "field(value)" request and failed, instead of falling back to "field()".

If this was a democracy, I'd vote for putting the more tolerant code back in.

Thanks,
-Kay

Replies:
Re: "Invalid request" for simply "pvget ThePV" when all other requests seem fine Michael Davidsaver
References:
"Invalid request" for simply "pvget ThePV" when all other requests seem fine Kasemir, Kay
Re: "Invalid request" for simply "pvget ThePV" when all other requests seem fine Andrew Johnson
Re: "Invalid request" for simply "pvget ThePV" when all other requests seem fine Kasemir, Kay
Re: "Invalid request" for simply "pvget ThePV" when all other requests seem fine Andrew Johnson

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