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From: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Date: Mon, 9 Nov 2020 11:32:12 +0000
Message-ID: 
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Subject: Re: psycopg3 and adaptation choices
To: Vladimir Ryabtsev <greatvovan@gmail.com>
Cc: Adrian Klaver <adrian.klaver@aklaver.com>, psycopg@postgresql.org
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On Mon, 9 Nov 2020 at 02:49, Vladimir Ryabtsev <greatvovan@gmail.com> wrote=
:
>
> A wild idea: support both client-side (like in psycopg2) and server-side =
binding. Keep old '%s' syntax and provide a separate method for client-side=
 binding (not in 'cur.execute()'). This could alleviate cases like paramete=
rs roundtripping and other cases of safe query composition. At the same tim=
e use '$N' for true server-side binding.
> Is it an overcomplication or there are valid use-cases of that?

Such a thing exists already: there is a client-side binding library,
which is pretty much a direct porting of the psycopg2.sql module
(https://www.psycopg.org/docs/sql.html). Using that facility, you can
compose argument client-side with `query =3D sql.SQL("select {},
%s").format("hello")` and pass the above to `cursor.execute(query,
[42]). It uses `{}` and `{name}`-style parameters to bind client-side
so it leaves %s placeholders untouched for execute().

In psycopg3 I've made it slightly easier to use by letting
`SQL.format()` to accept any Python object, and automatically wrapping
it into a `Literal()` object, whereas in psycopg2 `format()` only
accepted "`Composible`" objects, and you should have written the above
as `sql.SQL("select {}, %s").format(Literal("hello"))`.

-- Daniele