How to use ARRAY of INET in flask-sqlalchemy? - postgresql

Question

I have a user model with array of ips field in my flask application. I want to use postgresql array of inet type:
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy.dialects.postgresql import ARRAY, INET, Integer, Unicode, Column
db = SQLAlchemy()
class User(db.Model):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
login = Column(Unicode(15))
password = Column(Unicode(34))
name = Column(Unicode(100))
permitted_ips = Column(ARRAY(INET))
But when i make query i get bad answer:
user = User.query.get(84)
print user.permitted_ips
#['{', '1', '7', '2', '.', '2', '0', '.', '2', '5', '.', '2', ',', '1', '7', '2', '.', '2', '0', '.', '2', '5', '.', '3', '}']
instead of ['172.20.25.2', '172.20.25.3']. Current version of sqlalchemy is 0.9.10. I tried the latest one but result was the same. Is it possible to fix that?

Answer 1

I found that Arrays are not parsed automatically so you need to create a generic type caster with psycopg2 library.
# needed imports
from psycopg2 import STRING
from psycopg2.extensions import register_type, new_array_type
Registering the array type, it will be done one time.
# to see the oid of inet. As pointed out by #univerio the oid should never
# change, so you don't need to fetch it every time your app starts.
tp = db.engine.execute("select typarray from pg_type where typname = 'inet'")
print(tp.fetchone())
# (1041,)
# registering the array type
register_type(new_array_type((1041,), 'INET[]', STRING))
Now you can fetch the array and it will be parsed properly.
# fetch data
ips = db.engine.execute("select permitted_ips from users where id = 1")
print(ips.fetchone()[0])
# ['172.20.25.2', '172.20.25.3'].