Re: [PATCHES] libpq type system 0.9a

Tom Lane wrote:
> Andrew Chernow <ac@esilo.com> writes:
>> PGresult *PQresultDup(
>>    PGconn *conn,
>>    PGresult *res,
>>    int ntups,
>>    int numAttributes,
>>    PGresAttDesc *attDescs);
> 
> I don't understand why this is a "dup" operation.  How can you "dup"
> if you are specifying a new tuple descriptor?  I'd have expected
> something like
> 
> PGresult *PQmakeResult(PGconn *conn, int numAttributes, PGresAttDesc *attDescs)
> 
> producing a zero-row PGRES_TUPLES_OK result that you can then load with
> data via PQresultSetFieldValue calls.  (Even the conn argument is a bit
> of a wart, but I think we probably need it so we can copy some of its
> private fields.)
> 
> Copying an existing PGresult might have some use too, but surely that
> can't change its tuple descriptor.
> 
>             regards, tom lane
> 

Yeah, "dup" wasn't the best name.

You need more arguments to makeresult though, since you reomved the 
'source' result.  You need binary, cmdStatus, noticeHooks and 
client_encoding.

PQmakeResult(conn,  PQcmdStatus(res),  PQbinaryTuples(res),  ?client_encoding?,  ?noticeHooks?,  ntups, /* this
interactswith setfieldvalue */  numAttributes,  attDescs);
 

For client_encoding and noticeHooks, the conn can be NULL.  Previously, 
we copied this info from the source result when conn was NULL.
> producing a zero-row PGRES_TUPLES_OK result that you can then>load with data via PQresultSetFieldValue calls.
I like this idea but you removed the 'ntups' argument.  There is no way 
to adjust ntups after the makeresult call, its a private member and 
setfieldvalue has no concept of incrementing ntups.  Since you are not 
appending a tuple like pqAddTuple, or inserting one, you can't increment 
ntups in setfieldvalue.

But, you could have a function like PQresultAddEmptyTuple(res) which 
would have to be called before you can set field values on a tup_num. 
The empty tuple would grow tuples when needed and increment ntups.  The 
new tuple would be zerod (all NULL values).

....something like below

res = PQmakeResult(...);
for(ntups)
{  PQresultAddEmptyTuple(res); // or PQresultMakeEmptyTuple?  for(nfields)    PQresultSetFieldValue(res, tup_num,
field_num,....);
 
}


-- 
Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/