Global init

import cassio

cassio.init(...)

The purpose of this statement is to set a globally-available cassandra.cluster.Session, together with a keyspace name, as the default database connection for all subsequent CassIO instantiations. Once you have run init(...), you do not need to specify the DB anymore, e.g.

table = cassio.table.MetadataCassandraTable(table="my_table")

reader = cassio.db_reader.MultiTableCassandraReader(
    field_mapper={"v": ("t", "c")},
    admit_nulls=False,
)

Of course, you can still specify the parameters session and/or keyspace when creating the objects, in which case the latter will take precedence (for example, you may set the Session through init and then choose different keyspaces for various objects).

The init(...) can be invoked in several ways -- some of which exemplified below; no matter what the call signature, the invocation results in a session and/or a keyspace being set as defaults.

Example signatures

You have a Session and a Keyspace prepared beforehand:

import cassandra
cluster = cassandra.cluster.Cluster(...)
session = cluster.connect()
cassio.init(session=session, keyspace="my_k")

You have the connection parameters to a Cassandra cluster:

cassio.init(
    contact_points=['127.0.0.1'],
    username='u',
    password='p',
)

You have the credentials to an Astra DB instance:

cassio.init(database_id="abcd0123-...", token="AstraCS:...")

There are suitable environment variables available (e.g. CASSANDRA_CONTACT_POINTS, or the combination ASTRA_DB_APPLICATION_TOKEN plus ASTRA_DB_DATABASE_ID):

cassio.init(auto=True)

For more, try help cassio.init in a Python REPL.

Usage

Note that the global defaults thus set are consulted at constructor time by the various abstractions (e.g. the tables): so the following interaction, for example,

cassio.init(session=S1, keyspace=K1)
my_table = cassio.table.PlainCassandraTable(table="my_table")
cassio.init(session=S2, keyspace=K2)
table.put(row_id="x", body_blob="y")

does result in a table, with a row, in session S1: my_table will never be aware of the second init(...).

Accessing the session/keyspace

You can access the globally set DB connection at any time:

s = cassio.config.resolve_session()
k = cassio.config.resolve_keyspace()

These are an ordinary cassandra.cluster.Session and an ordinary string (unless, if not set yet, None), which can be used e.g. to execute CQL statements.

s.execute(f"DROP TABLE IF EXISTS {k}.table_name;")