Connections (experimental)
Connections are experimental and aimed to ease the use of multiple sessions with cqlengine. Connections can be set on a model class, per query or using a context manager.
Register a new connection
To use cqlengine, you need at least a default connection. This is currently done automatically under the hood with connection.setup
. If you want to use another cluster/session, you need to register a new cqlengine connection. You register a connection with register_connection()
Copyfrom cassandra.cqlengine import connection connection.setup(['127.0.0.1') connection.register_connection('cluster2', ['127.0.0.2'])
Change the default connection
You can change the default cqlengine connection on registration:
Copyfrom cassandra.cqlengine import connection connection.register_connection('cluster2', ['127.0.0.2'] default=True)
or on the fly using set_default_connection()
Copyconnection.set_default_connection('cluster2')
Unregister a connection
You can unregister a connection using unregister_connection()
:
Copyconnection.unregister_connection('cluster2')
Management
When using multiples connections, you also need to sync your models on all connections (and keyspaces) that you need operate on. Management commands have been improved to ease this part. Here is an example:
Copyfrom cassandra.cqlengine import management keyspaces = ['ks1', 'ks2'] conns = ['cluster1', 'cluster2'] # registers your connections # ... # create all keyspaces on all connections for ks in keyspaces: management.create_simple_keyspace(ks, connections=conns) # define your Automobile model # ... # sync your models management.sync_table(Automobile, keyspaces=keyspaces, connections=conns)
Connection Selection
cqlengine will select the default connection, unless your specify a connection using one of the following methods.
Default Model Connection
You can specify a default connection per model:
Copyclass Automobile(Model): __keyspace__ = 'test' __connection__ = 'cluster2' manufacturer = columns.Text(primary_key=True) year = columns.Integer(primary_key=True) model = columns.Text(primary_key=True) print len(Automobile.objects.all()) # executed on the connection 'cluster2'
QuerySet and model instance
You can use the using()
method to select a connection (or keyspace):
CopyAutomobile.objects.using(connection='cluster1').create(manufacturer='honda', year=2010, model='civic') q = Automobile.objects.filter(manufacturer='Tesla') autos = q.using(keyspace='ks2, connection='cluster2').all() for auto in autos: auto.using(connection='cluster1').save()
Context Manager
You can use the ContextQuery as well to select a connection:
Copywith ContextQuery(Automobile, connection='cluster1') as A: A.objects.filter(manufacturer='honda').all() # executed on 'cluster1'
BatchQuery
With a BatchQuery, you can select the connection with the context manager. Note that all operations in the batch need to use the same connection.
Copywith BatchQuery(connection='cluster1') as b: Automobile.objects.batch(b).create(manufacturer='honda', year=2010, model='civic')