CQL Engine Exception about a connection name not existing in registry

Question

I get the following exception while trying to connect to a Cassandra DB using a Python Cassandra-Driver client running on Windows 2012 Server R2 - 64 bit. I could get this working on my personal laptop but not a machine that is hosted on Azure. I am sure I am missing some dependencies but just unsure about what they are.

File "C:\Python\Python35-32\lib\site-packages\cassandra\cqlengine\connection.py", line 190, in get_connection raise CQLEngineException("Connection name '{0}' doesn't exist in the registry.".format(name)) Cassandra.cqlengine.CQLEngineException: Connection name '' doesnt exist in the registry.

Talmudist

This happens with cassandra-driver-3.7. When I downgraded the version to 3.6 and 3.5 things started working. My laptop has 3.5 on it and the new machine had 3.7 version. Still not sure if there is such a big change between the minor updates of driver. – Talmudist

Answer 1

This is a known issue and will be fixed in the next release (3.8.0): https://datastax-oss.atlassian.net/browse/PYTHON-649

As a workaround, you can see if it's possible to setup the connection before any UDT model definition or downgrade to 3.6.

Addle

This seems to still be an issue as of 3.12.0 Did it get sorted out by any chance? (granted on line 241) – Anneal

Answer 2

I also run into this (cassandra-driver 3.13), since I had to decouple cassandra shared models from some flask apps and other simple components for batch processing. What I eventually found it's working is in the snippet below (important bits are register_connection and set_default_connection functions):

import os

from cassandra.cluster import Cluster
from cassandra.cqlengine.connection import register_connection, set_default_connection
from flask_cqlalchemy import CQLAlchemy

cqldb = CQLAlchemy()
_keyspace = os.environ.get('CASSANDRA_KEYSPACE', 'persistent')
_hosts = [os.environ.get('CASSANDRA_HOST', 'cassandra')]
_port = os.environ.get('CASSANDRA_PORT', 9042)


def cassandra_session_factory():
    cluster = Cluster(_hosts, port=_port)
    session = cluster.connect()
    session.row_factory = dict_factory
    session.execute("USE {}".format(_keyspace))
    return session


_session = cassandra_session_factory()
register_connection(str(_session), session=_session)
set_default_connection(str(_session))


class MyModel(cqldb.Model):
    """
    Object representing the `model` column family in Cassandra
    """
    __keyspace__ = _keyspace

    session = _session
    session.default_fetch_size = 1000

    myfield = cqldb.columns.Text(primary_key=True, required=True)

Nazareth