Re: FDW: possible resjunk columns in AddForeignUpdateTargets

Tom Lane wrote:
> Albe Laurenz <laurenz.albe@wien.gv.at> writes:
>> I have a question concerning the Foreign Data Wrapper API:
>> I find no mention of this in the documentation, but I remember that
>> you can only add a resjunk column that matches an existing attribute
>> of the foreign table and not one with an arbitrary name or
>> definition.
> 
>> Ist that right?
> 
> I don't recall such a limitation offhand.  It's probably true that
> you can't create Vars that don't match some declared column of the
> table, but that doesn't restrict what you put into resjunk columns
> AFAIR.

I am confused, probably due to lack of knowledge.

What I would like to do is add a custom resjunk column
(e.g. a bytea) in AddForeignUpdateTargets that carries a row identifier
from the scan state to the modify state.
Would that be possible? Can I have anything else than a Var
in a resjunk column?

Yours,
Laurenz Albe