public inbox for [email protected]  

help / color / mirror / Atom feed

From: Daniele Varrazzo <[email protected]>
To: [email protected]
Subject: Executing on the connection?
Date: Wed, 2 Dec 2020 11:20:16 +0000
Message-ID: <CA+mi_8Yc92bX3qhTqXq4LkGyn5VmQj6uRAcVebpqt398Tm4EJA@mail.gmail.com> (raw)

Hello,

if there is a thing that people approaching psycopg find confusing is
the connection/cursor duality. The connection object as a wrapper for
the database connection is clear to understand for anyone who has used
psql. But the cursor as a means to give command is spurious: you can
give commands but all the cursors are serialised, not parallelised, on
the same connection, and it isn't useful for transactions either...

The only unique thing a cursor has is to hold a result and consume it;
for the rest it doesn't own neither the postgres session nor the
transaction. But it gives them command. Weird.

You are surely familiar with the psycopg2 usage pattern:

    conn = psycopg2.connect(dsn)
    cur = conn.cursor()
    cur.execute(query, params):
    for record in cur:
        ... # do something

The cursor() can take parameters, e.g. to create server-side "named"
cursors, but most often people will use the standard client-side
cursor, which is a lightweight object, little more than a wrapper for
a PGresult.

One little change I've made to psycopg3 cursors is to make it return
"self" on execute() (it currently returns None, so it's totally
unused). This allows chaining a fetch operation right after execute,
so the pattern above can be reduced to:

    conn = psycopg3.connect(dsn)
    cur = conn.cursor()
    record = cur.execute(query, params).fetchone()
    # or
    for record in cur.execute(query, params):
        ... # do something

And of course nastymess such as:

    conn.cursor().execute(query).fetchone()
    psycopg3.connect(dsn).cursor().execute(query).fetchone()

But, taste.

I'm toying with the idea of adding a 'connection.execute(query,
[params])' methd, which would basically just create a cursor
internally, query on it, and return it. No parameter could be passed
to the cursor() call, so it could only create the most standard,
client-side cursor (or whatever the default for the connection is, if
there is some form of cursor_factory, which hasn't been implemented in
psycopg3 yet). For anything more fancy, cursor() should be called
explicitly.

As a result people could use:

    conn = psycopg3.connect(dsn)
    record = conn.execute(query, params).fetchone()
    # or
    for record in conn.execute(query, params):
        ... # do something

No other methods bloating the connection interface: no executemany(),
copy(), callproc (actually there will be no callproc at all in
psycopg3: postgres has no fast path for function call and too much
semantics around stored procedure that a single callproc() couldn't
cover).

Being the cursor client-side, its close() doesn't actually do anythin
apart from making it unusable, so just disposing of it without calling
close() is totally safe.

Thoughts?

Cheers!

-- Daniele

view thread (13+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected]
  Subject: Re: Executing on the connection?
  In-Reply-To: <CA+mi_8Yc92bX3qhTqXq4LkGyn5VmQj6uRAcVebpqt398Tm4EJA@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox