Re: COPY as a set returning function

On Tue, Jan 31, 2017 at 3:05 AM, Corey Huinker <corey(dot)huinker(at)gmail(dot)com> wrote:
> On Fri, Jan 27, 2017 at 9:42 PM, Peter Eisentraut
> <peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
>>
>> On 1/25/17 8:51 PM, Corey Huinker wrote:
>> > # select * from copy_srf('echo "x\ty"',true) as t(x text, y text);
>>
>> I find these parameters weird. Just looking at this, one has no idea
>> what the "true" means. Why not have a "filename" and a "program"
>> parameter and make them mutually exclusive?
>
>
> It was done that way to match the parameters of BeginCopyFrom() and it could
> easily be changed.
>
> I suppose I could have written it as:
>
> select * from copy_srf(filename => 'echo "x\ty"', is_program => true) as t(x
> text, y text);
>
>
> But this goes to the core of this patch/poc: I don't know where we want to
> take it next.
>
> Options at this point are:
> 1. Continue with a SRF, in which case discussions about parameters are
> completely valid.
> 2. Add a RETURNING clause to COPY. This would dispense with the parameters
> problem, but potentially create others.
> 3. Add the TupDesc parameter to BeginCopyFrom, make sure all data structures
> are visible to an extension, and call it a day. If someone wants to write an
> extension that makes their own copy_srf(), they can.
> 4. Someone else's better idea.

Here is a 4: Refactoring BeginCopyFrom so as instead of a Relation are
used a TupleDesc, a default expression list, and a relation name. You
could as well make NextCopyFrom() smarter so as it does nothing if no
expression contexts are given by the caller, which is the case of your
function here. To be honest, I find a bit weird to use
NextCopyFromRawFields when there is already a bunch of sanity checks
happening in NextCopyFrom(), where you surely want to have them
checked even for your function.

Looking at the last patch proposed, I find the current patch proposed
as immature, as rsTupDesc basically overlaps with the relation a
caller can define in BeginCopyFrom(), so marking this patch as
"returned with feedback".
--
Michael