User Defined Types

Cassandra 2.1 introduced user-defined types (UDTs). You can create a new type through CREATE TYPE statements in CQL:

CREATE TYPE address (street text, zip int);

Version 2.1 of the Python driver adds support for user-defined types.

Registering a Class to Map to a UDT

You can tell the Python driver to return columns of a specific UDT as instances of a class by registering them with your Cluster instance through Cluster.register_user_type():

cluster = Cluster(protocol_version=3)
session = cluster.connect()
session.set_keyspace('mykeyspace')
session.execute("CREATE TYPE address (street text, zipcode int)")
session.execute("CREATE TABLE users (id int PRIMARY KEY, location frozen<address>)")

# create a class to map to the "address" UDT
class Address(object):

    def __init__(self, street, zipcode):
        self.street = street
        self.zipcode = zipcode

cluster.register_user_type('mykeyspace', 'address', Address)

# insert a row using an instance of Address
session.execute("INSERT INTO users (id, location) VALUES (%s, %s)",
                (0, Address("123 Main St.", 78723)))

# results will include Address instances
results = session.execute("SELECT * FROM users")
row = results[0]
print row.id, row.location.street, row.location.zipcode

Using UDTs Without Registering Them

Although it is recommended to register your types with Cluster.register_user_type(), the driver gives you some options for working with unregistered UDTS.

When you use prepared statements, the driver knows what data types to expect for each placeholder. This allows you to pass any object you want for a UDT, as long as it has attributes that match the field names for the UDT:

cluster = Cluster(protocol_version=3)
session = cluster.connect()
session.set_keyspace('mykeyspace')
session.execute("CREATE TYPE address (street text, zipcode int)")
session.execute("CREATE TABLE users (id int PRIMARY KEY, location frozen<address>)")

class Foo(object):

    def __init__(self, street, zipcode, otherstuff):
        self.street = street
        self.zipcode = zipcode
        self.otherstuff = otherstuff

insert_statement = session.prepare("INSERT INTO users (id, location) VALUES (?, ?)")

# since we're using a prepared statement, we don't *have* to register
# a class to map to the UDT to insert data.  The object just needs to have
# "street" and "zipcode" attributes (which Foo does):
session.execute(insert_statement, [0, Foo("123 Main St.", 78723, "some other stuff")])

# when we query data, UDT columns that don't have a class registered
# will be returned as namedtuples:
results = session.execute("SELECT * FROM users")
first_row = results[0]
address = first_row.location
print address  # prints "Address(street='123 Main St.', zipcode=78723)"
street = address.street
zipcode = address.street

As shown in the code example, inserting data for UDT columns without registering a class works fine for prepared statements. However, you must register a class to insert UDT columns with unprepared statements.* You can still query UDT columns without registered classes using unprepared statements, they will simply return namedtuple instances (just like prepared statements do).

* this applies to parameterized unprepared statements, in which the driver will be formatting parameters – not statements with interpolated UDT literals.