David,
That said, I am curious as to the education flow a developer, not linking in
this specific header to their code, would go through in order to learn about
type OIDs and make use of them in their project. Maybe that flow is good,
maybe not. It's a rare flow and there are many things to do in the project.
So my curiosity may not get satiated. As you brought this up and are invested
in the outcome you have more motivation than probably anyone else to dive into
it and make concrete suggestions for change.
Any project using the PostgreSQL C API to implement an interface/module for
another programming language will need to implement basic SQL handling
functions to prepare, execute, fetch rows, AND introspect SQL statements parts
like column information (name, type).
We have for ex a SQL handler class in Genero BDL, providing following methods:
DEFINE h base.SqlHandle
LET h = base.SqlHandle.create()
CALL h.prepare("SELECT ....")
CALL h.open()
DISPLAY h.getResultType(1) : type name of column #1
DISPLAY h.getResultType(2) : type name of column #2
...
About the PQftype() doc, the header file catalog/pg_type_d.h is mentioned, but
I think it is missing the fact that type OID constants can be recognized in
that header file, with the "OID" suffix.
While I understand that it's additional work on doc maintenance, I would in
fact expect an exhaustive list of built-in data type ids just like in:
https://learn.microsoft.com/en-us/sql/odbc/reference/appendixes/sql-data-types?view=sql-server-ver16
https://dev.mysql.com/doc/c-api/8.4/en/c-api-prepared-statement-type-codes.html
https://www.ibm.com/docs/en/informix-servers/15.0.0?topic=constants-sql-data-type#ids_esqlc_0123__sii-03-97666
But I can understand that this is maybe not natural for PostgreSQL
implementors, because of the flexible data type system and the fact that even
built-in type ids are generated.
Seb
________________________________
From: David G. Johnston <[email protected]>
Sent: Thursday, March 20, 2025 5:25 PM
To: Sebastien Flaesch <[email protected]>
Cc: Tom Lane <[email protected]>; Adrian Klaver <[email protected]>; M
Tarkeshwar Rao <[email protected]>; [email protected]
<[email protected]>
Subject: Re: After upgrading libpq, the same function(PQftype) call returns a
different OID
EXTERNAL: Do not click links or open attachments if you do not recognize the
sender.
On Thu, Mar 20, 2025 at 8:42 AM Sebastien Flaesch
<[email protected]<mailto:[email protected]>> wrote:
/*
* Backwards compatibility for ancient random spellings of pg_type OID macros.
* Don't use these names in new code.
*/
#define CASHOID MONEYOID
#define LSNOID PG_LSNOID
#define BOOLOID 16
#define BYTEAOID 17
#define CHAROID 18
#define NAMEOID 19
#define INT8OID 20
#define INT2OID 21
#define INT2VECTOROID 22
#define INT4OID 23
#define REGPROCOID 24
If I am missing something, then please point me to the correct .h file that
contains #define constants without this scary comment.
OR.... ( I guess I start to understand the code... ) it this comment only for:
Yes, that blank line separating LSNOID and BOOLOID blocks the comment from
applying to the items after the blank line. That is a fairly common
convention, using whitespace to break things up. Also, assigning one macro to
another is quite distinct from assigning a constant to a name; making the
"backward compatibility" aspect of this comment only meaningfully apply to
those two items.
And sorry if I consider constant names like these (without any prefix such as
PG_TYPE_)
We spelled PG_TYPE_ as OID and put it on the end. A boolean as an object is
by definition a type. Context clues are important, not every pattern gets
spelled out in prose.
#define BOOLOID 16
#define BYTEAOID 17
#define CHAROID 18
#define NAMEOID 19
#define INT8OID 20
#define INT2OID 21
Arrogance does not help here, clarity and better API doc would.
To my knowledge the current API doc for this hasn't had any comments of this
sort for a very long time. All documentation can be improved because every
reader comes at it from a different starting point. Do you have a concrete
suggestion for what you think should be changed, and why? My take away from
this thread is that a single report isn't usually enough to go searching hard
for ways to tweak the documentation for readability; nor has this one pointed
out any outright errors to be fixed. In short, we expect that some subset of
readers will ask us questions on the mailing list because that is the reality
of things.
That said, I am curious as to the education flow a developer, not linking in
this specific header to their code, would go through in order to learn about
type OIDs and make use of them in their project. Maybe that flow is good,
maybe not. It's a rare flow and there are many things to do in the project.
So my curiosity may not get satiated. As you brought this up and are invested
in the outcome you have more motivation than probably anyone else to dive into
it and make concrete suggestions for change.
All that said, a comment at the top of what is probably the most important
section of the header seems warranted. Even if it is just mostly formality.
Mentioning the constant-ness of the integers should be part of that.
David J.
