Re: [Pypgsql-users] Re: [ANN] pyPgSQL 2.1 released

[Gerhard <ger...@gm...>]

* pa...@bo... <pa...@bo...> [2002-06-05 17:08 -0000]:
> On Wed, 5 Jun 2002 18:40:11 +0200 Gerhard Häring wrote:
> >CC-ing to pypgsql-users list, maybe other users have comments on this issue,
> >too.
> 
> [Arrays vs. 'IN']
> 
> >QUERY: DECLARE PgSQL_08120A6C CURSOR FOR select * from cages where name
> >       in '{"mammals","apes"}'
> >
> >... which obviously cannot work. The reason is that if pyPgSQL encounters a
> >tuple or a list in the statement parameters, it will quote them suitable for
> >use as an ARRAY. Unfortunately, the ARRAY syntax is different from what you
> >would need for the IN operator in SQL.
> 
> Right, and there's no way of knowing what the database engine expects for
> that parameter until it has parsed the statement.

Unless you also parse at the client side, which I'd rather not ;-)

There might be a solution with controlling the behaviour using a flag in the
cursor object, for example.

> I suppose there isn't a way of getting type information from PostgreSQL about
> parameters - indeed, does PostgreSQL actually support parameters in the way
> that other database systems do?

You mean prepared statements? No, PostgreSQL doesn't currently support these.
All it gets is a query string. From what I hear on IRC and on
postgresql-hackers, people are working on prepared statements.

Unfortunately, we'll have a problem with them and pyPgSQL, as as far as I see,
prepared statements don't play nice with the DB-API 2.0 'format' and 'pyformat'
parameter quoting styles. I believe that the 'qmark' or 'numeric' styles are
designed exactly for prepared statement use. It might be possible to rewrite
the query and continue using our 'pyformat' style, but I haven't tried, yet.

> > [Unicode patch] 
> That would be great. Where XML data and PostgreSQL come together, it quickly
> becomes a requirement to handle the data gracefully or transparently,
> although I suspect that many database systems still struggle with Unicode.

Hopefully, pyPgSQL with PostgreSQL works fine. PostgreSQL can even use the
UTF-8 encoding at server side. With the Unicode patch and appropriate
parameters for the connect() call, you should be able to use full Unicode:

>>> from pyPgSQL import PgSQL
>>> conn = PgSQL.connect(client_encoding="utf-8", unicode_results=1)
>>> cursor = conn.cursor()
>>> cursor.execute("insert into test(name) values (%s)", unicode("Österreich", "latin1"))
>>> cursor.execute("select * from test")
>>> res = cursor.fetchone()
>>> print repr(res.name)
u'\xd6sterreich'

Btw. the Unicode support that PySQLite recently gained is based on the same
patch, and it includes an example for mass-importing Freshmeat project data
from XML into a database. As you said, XML is Unicode-based, so this is a
relatively practical example, I hope.

Gerhard
-- 
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