deb-python-cassandra-driver/docs/topics/columns.rst

Columns

Users of versions < 0.4, please read this post before upgrading: Breaking Changes

cqlengine.columns

Stores arbitrary bytes (no validation), expressed as hexadecimal :

columns.Bytes()

Stores a US-ASCII character string :

columns.Ascii()

Stores a UTF-8 encoded string :

columns.Text()

options

~columns.Text.min_length

Sets the minimum length of this string. If this field is not set , and the column is not a required field, it defaults to 0, otherwise 1.

~columns.Text.max_length

Sets the maximum length of this string. Defaults to None

Stores an integer value :

columns.Integer()

Stores a datetime value.

Python's datetime.now callable is set as the default value for this column :

columns.DateTime()

Stores a type 1 or type 4 UUID.

Python's uuid.uuid4 callable is set as the default value for this column. :

columns.UUID()

Stores a boolean True or False value :

columns.Boolean()

Stores a floating point value :

columns.Float()

options

~columns.Float.double_precision

If True, stores a double precision float value, otherwise single precision. Defaults to True.

Stores a variable precision decimal value :

columns.Decimal()

Collection Type Columns

CQLEngine also supports container column types. Each container column requires a column class argument to specify what type of objects it will hold. The Map column requires 2, one for the key, and the other for the value

Example

class Person(Model):
    first_name  = columns.Text()
    last_name   = columns.Text()

    friends     = columns.Set(columns.Text)
    enemies     = columns.Set(columns.Text)
    todo_list   = columns.List(columns.Text)
    birthdays   = columns.Map(columns.Text, columns.DateTime)

Stores a set of unordered, unique values. Available only with Cassandra 1.2 and above :

columns.Set(value_type)

options

~columns.Set.value_type

The type of objects the set will contain

~columns.Set.strict

If True, adding this column will raise an exception during save if the value is not a python set instance. If False, it will attempt to coerce the value to a set. Defaults to True.

Stores a list of ordered values. Available only with Cassandra 1.2 and above :

columns.List(value_type)

options

~columns.List.value_type

The type of objects the set will contain

Stores a map (dictionary) collection, available only with Cassandra 1.2 and above :

columns.Map(key_type, value_type)

options

~columns.Map.key_type

The type of the map keys

~columns.Map.value_type

The type of the map values

Column Options

Each column can be defined with optional arguments to modify the way they behave. While some column types may define additional column options, these are the options that are available on all columns:

BaseColumn.primary_key

If True, this column is created as a primary key field. A model can have multiple primary keys. Defaults to False.

In CQL, there are 2 types of primary keys: partition keys and clustering keys. As with CQL, the first primary key is the partition key, and all others are clustering keys, unless partition keys are specified manually using BaseColumn.partition_key

BaseColumn.partition_key

If True, this column is created as partition primary key. There may be many partition keys defined, forming a composite partition key

BaseColumn.index

If True, an index will be created for this column. Defaults to False.

Note: Indexes can only be created on models with one primary key

BaseColumn.db_field

Explicitly sets the name of the column in the database table. If this is left blank, the column name will be the same as the name of the column attribute. Defaults to None.

BaseColumn.default

The default value for this column. If a model instance is saved without a value for this column having been defined, the default value will be used. This can be either a value or a callable object (ie: datetime.now is a valid default argument).

BaseColumn.required

If True, this model cannot be saved without a value defined for this column. Defaults to True. Primary key fields cannot have their required fields set to False.

BaseColumn.clustering_order

Defines CLUSTERING ORDER for this column (valid choices are "asc" (default) or "desc"). It may be specified only for clustering primary keys - more: http://www.datastax.com/docs/1.2/cql_cli/cql/CREATE_TABLE#using-clustering-order