From: Richard Jones <rich@annexia.org>
To: caml-list@inria.fr
Subject: Re: [Caml-list] Type-safe interface to Postgres's SQL
Date: Sat, 18 Feb 2006 16:01:53 +0000 [thread overview]
Message-ID: <20060218160151.GA28024@furbychan.cocan.org> (raw)
In-Reply-To: <20060131140733.GA31772@furbychan.cocan.org>
On Tue, Jan 31, 2006 at 02:07:33PM +0000, Richard Jones wrote:
> (2) PostgreSQL doesn't track NULL types properly so we have to do a
> bit of non-trivial guesswork to try to find out if a database field
> could contain a NULL or not (and therefore whether to map its type to
> 'a or 'a option). For parameters this isn't possible at all, so all
> parameter variables must have an option type. For result fields, it
> is usually possible to tell if the result corresponds to a known
> column in the database, which is the case in ninety percent of
> queries.
FWIW I have solved this problem with a small syntactic change. You
now use $varname when you don't want NULLs and $?varname when you
do.[1] A modified example program is attached.
You can also download the full program from here:
http://merjis.com/tmp/pgocaml-0.2.tar.gz
Rich.
[1] It is still possible to insert a NULL into a NOT NULL field, as
was the case before, but I can't see any way to solve that without
rewriting Postgres.
----------------------------------------------------------------------
(* Example program using typesafe calls to PostgreSQL.
* $Id: test.ml,v 1.4 2006/02/18 15:54:06 rich Exp $
*)
open Printf
let () =
let dbh = PGOCaml.connect () in
PGSQL_EXECUTE_ON_COMPILE(dbh) "create temporary table employees (
id serial not null primary key,
name text not null,
salary int4 not null,
email text
)";
let insert name salary email =
PGSQL(dbh) "insert into employees (name, salary, email)
values ($name, $salary, $?email)"
in
insert "Ann" 10_000_l None;
insert "Bob" 45_000_l None;
insert "Jim" 20_000_l None;
insert "Mary" 30_000_l (Some "mary@example.com");
let rows = PGSQL(dbh) "select id, name, salary, email from employees" in
List.iter (
fun (id, name, salary, email) ->
let email = match email with Some email -> email | None -> "-" in
printf "%ld %S %ld %S\n" id name salary email
) rows;
PGOCaml.close dbh
--
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com
next prev parent reply other threads:[~2006-02-18 16:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-31 14:07 Richard Jones
2006-02-18 16:01 ` Richard Jones [this message]
2006-01-31 16:43 [Caml-list] " Quinn, Chris
2006-01-31 17:51 ` brogoff
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