Re: Listening for postgres NOTIFY with django.db - adding support for connection.fileno()

[Fábio Molinar]

Thank you sir, that's what I was hoping to find! :)

Yours sincerely,

*Fábio Thomaz Molinar*


Em ter, 1 de jan de 2019 às 15:10, Florian Apolloner 
escreveu:

> Hi,
>
> On Monday, December 31, 2018 at 12:38:31 PM UTC+1, Fábio Molinar wrote:
>>
>> Is this currently not supported or am I missing something? I though that
>> the django.db is kind of just a wrapper around the actual psycopg2 library.
>> So I wonder why I can't use the fileno() method on it.
>>
>
> django.db.connection provides a common interface for all databases, the
> underlying actual connection is stored as connection attribute as seen in
> https://github.com/django/django/blob/master/django/db/backends/base/base.py#L194
> -- I hope this helps.
>
> cheers,
> Florian
>
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Re: Listening for postgres NOTIFY with django.db - adding support for connection.fileno()

[Florian Apolloner]

Hi,

On Monday, December 31, 2018 at 12:38:31 PM UTC+1, Fábio Molinar wrote:
>
> Is this currently not supported or am I missing something? I though that 
> the django.db is kind of just a wrapper around the actual psycopg2 library. 
> So I wonder why I can't use the fileno() method on it.
>

django.db.connection provides a common interface for all databases, the 
underlying actual connection is stored as connection attribute as seen in 
https://github.com/django/django/blob/master/django/db/backends/base/base.py#L194
 
-- I hope this helps.

cheers,
Florian

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Listening for postgres NOTIFY with django.db - adding support for connection.fileno()

[Fábio Molinar]

Hi, 

I have a custom method on my model manager that allows me to listen for 
notifications from modifications on the DB using postgreSQL. A short 
version of this code looks like this:

def listen_for_notify(self):
import select
import psycopg2
import psycopg2.extensions

from django.conf import settings

db_data = settings.DATABASES['default']
listened = None
returned_empty = None
search_timeout = 15

conn = psycopg2.connect(dbname=db_data['NAME'], 
user=db_data['USER'], password=db_data['PASSWORD'], host=db_data['HOST'], 
port=db_data['PORT'])

conn.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
curs = conn.cursor()
curs.execute("LISTEN default;") 

timeout = timezone.now() + timezone.timedelta(0, search_timeout)
while timezone.now() < timeout:
time_diff = timeout - timezone.now()
if select.select([conn], [], [], float(time_diff.seconds)) == 
([], [], []):
listened = False
timeout = timezone.now()
else:
conn.poll()
while conn.notifies:
notify = conn.notifies.pop(0)
if notify.payload == "notified":
listened = True
returned_empty = False
timeout = timezone.now()
if notify.payload == 'search request returned empty':
listened = True
returned_empty = True
timeout = timezone.now()
curs.close()
conn.close()
return listened, returned_empty

It would be really nice if instead of using the psycopg2 library, I could 
use only django.db. Something like this:

def listen_for_notify(self):
from django.db import connection as conn

listened = None
returned_empty = None
search_timeout = 15

with conn.cursor() as curs
timeout = timezone.now() + timezone.timedelta(0, search_timeout)
while timezone.now() < timeout:
time_diff = timeout - timezone.now()
if select.select([conn], [], [], float(time_diff.seconds)) == ([], [], []):
listened = False
timeout = timezone.now()
else:
conn.poll()
while conn.notifies:
notify = conn.notifies.pop(0)
if notify.payload == "notified":
listened = True
returned_empty = False
timeout = timezone.now()
if notify.payload == 'search request returned empty':
listened = True
returned_empty = True
timeout = timezone.now()
return listened, returned_empty

I tried out the solution above using django.db, but it doesn't work because 
the django.db.connection object don't have a fileno() method.

Is this currently not supported or am I missing something? I though that 
the django.db is kind of just a wrapper around the actual psycopg2 library. 
So I wonder why I can't use the fileno() method on it.

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