Re: Using composite types in psycopg3

On Tue, 10 Nov 2020 at 21:59, Vladimir Ryabtsev <greatvovan(at)gmail(dot)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