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From: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Date: Wed, 11 Nov 2020 00:24:11 +0000
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Subject: Re: Using composite types in psycopg3
To: Vladimir Ryabtsev <greatvovan@gmail.com>
Cc: psycopg@postgresql.org
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On Tue, 10 Nov 2020 at 21:59, Vladimir Ryabtsev <greatvovan@gmail.com> wrote:

> psycopg2 returns the 'result' as a basic string, while
> in asyncpg and py-postgresql I have structured data
> (roughly 'List[Tuple[int, List[str]]]').
>
> I tried the same in psycopg3 and it is little bit better, but
> not entirely: it shows the outer list, the tuples inside it,
> but the innermost list is still represented as a basic string:
> '{one,"one more"}'.
>
> Is it something you are still working on? Any workarounds?
Yes: by obtaining data from the db in binary mode you can get
information about deeply nested objects. psycopg2 works only in text
mode, psycopg3 in both.

    In [1]: query = """
       ...: with test as (
       ...:     select 1 as id, 'one' val
       ...:     union all
       ...:     select 1, 'one more'
       ...:     union all
       ...:     select 2, 'two'
       ...: )
       ...: select array(
       ...:     select (id, array_agg(val))
       ...:     from test
       ...:     group by id
       ...: )"""

    In [2]: import psycopg3

    In [3]: from psycopg3.pq import Format

    In [4]: cnn = psycopg3.connect("")

    In [5]: cnn.cursor().execute(query).fetchone()[0]
    Out[5]: [('1', '{one,"one more"}'), ('2', '{two}')]

    In [6]: cnn.cursor(format=Format.BINARY).execute(query).fetchone()[0]
    Out[6]: [(1, ['one', 'one more']), (2, ['two'])]

Binary loading/dumping is not supported yet for all the data types,
but the plan is to cover all the builtins. Still not sure about the
interface to request text/binary results, or whether binary shouldn't
be the default as opposed to text. There is still ground to cover, but
we are getting there.

-- Daniele