cassandra.cqlengine.models - Table models for object mapping

Model

class cassandra.cqlengine.models.Model(**kwargs)

The initializer creates an instance of the model. Pass in keyword arguments for columns you’ve defined on the model.

class Person(Model):
    id = columns.UUID(primary_key=True)
    first_name  = columns.Text()
    last_name = columns.Text()

person = Person(first_name='Blake', last_name='Eggleston')
person.first_name  #returns 'Blake'
person.last_name  #returns 'Eggleston'

Model attributes define how the model maps to tables in the database. These are class variables that should be set when defining Model deriviatives.

__abstract__ = False

Optional. Indicates that this model is only intended to be used as a base class for other models. You can’t create tables for abstract models, but checks around schema validity are skipped during class construction.

__table_name__ = None

Optional. Sets the name of the CQL table for this model. If left blank, the table name will be the name of the model, with it’s module name as it’s prefix. Manually defined table names are not inherited.

__keyspace__ = None

Sets the name of the keyspace used by this model.

__default_ttl__ = None

__discriminator_value__ = None

Optional Specifies a value for the discriminator column when using model inheritance.

See Model Inheritance for usage examples.

Each table can have its own set of configuration options, including compaction. Unspecified, these default to sensible values in the server. To override defaults, set options using the model __options__ attribute, which allows options specified a dict.

When a table is synced, it will be altered to match the options set on your table. This means that if you are changing settings manually they will be changed back on resync.

Do not use the options settings of cqlengine if you want to manage your compaction settings manually.

See the list of supported table properties for more information.

__options__

For example:

class User(Model):
    __options__ = {'compaction': {'class': 'LeveledCompactionStrategy',
                                  'sstable_size_in_mb': '64',
                                  'tombstone_threshold': '.2'},
                   'read_repair_chance': '0.5',
                   'comment': 'User data stored here'}

    user_id = columns.UUID(primary_key=True)
    name = columns.Text()

or :

class TimeData(Model):
    __options__ = {'compaction': {'class': 'SizeTieredCompactionStrategy',
                                  'bucket_low': '.3',
                                  'bucket_high': '2',
                                  'min_threshold': '2',
                                  'max_threshold': '64',
                                  'tombstone_compaction_interval': '86400'},
                   'gc_grace_seconds': '0'}

The base methods allow creating, storing, and querying modeled objects.

create(**kwargs)

Create an instance of this model in the database.

Takes the model column values as keyword arguments.

Returns the instance.

if_not_exists()

Check the existence of an object before insertion. The existence of an object is determined by its primary key(s). And please note using this flag would incur performance cost.

if the insertion didn’t applied, a LWTException exception would be raised.

try:
    TestIfNotExistsModel.if_not_exists().create(id=id, count=9, text='111111111111')
except LWTException as e:
    # handle failure case
    print e.existing # existing object

This method is supported on Cassandra 2.0 or later.

save()

Saves an object to the database.

#create a person instance
person = Person(first_name='Kimberly', last_name='Eggleston')
#saves it to Cassandra
person.save()

update(**values)

Performs an update on the model instance. You can pass in values to set on the model for updating, or you can call without values to execute an update against any modified fields. If no fields on the model have been modified since loading, no query will be performed. Model validation is performed normally.

It is possible to do a blind update, that is, to update a field without having first selected the object out of the database. See Blind Updates

iff(**values)

Checks to ensure that the values specified are correct on the Cassandra cluster. Simply specify the column(s) and the expected value(s). As with if_not_exists, this incurs a performance cost.

If the insertion isn’t applied, a LWTException is raised

t = TestTransactionModel(text='some text', count=5)
try:
     t.iff(count=5).update('other text')
except LWTException as e:
    # handle failure

get(*args, **kwargs)

Returns a single object based on the passed filter constraints.

This is a pass-through to the model objects().:method:~cqlengine.queries.get.

filter(*args, **kwargs)

Returns a queryset based on filter parameters.

This is a pass-through to the model objects().:method:~cqlengine.queries.filter.

all()

Returns a queryset representing all stored objects

This is a pass-through to the model objects().all()

delete()

Deletes the object from the database

batch(batch_object)

Sets the batch object to run instance updates and inserts queries with.

See Batch Queries for usage examples

timeout(timeout)

Sets a timeout for use in save(), update(), and delete() operations

timestamp(timedelta_or_datetime)

Sets the timestamp for the query

ttl(ttl_in_sec)

Sets the ttl values to run instance updates and inserts queries with.

column_family_name(include_keyspace=True)

Returns the column family name if it’s been defined otherwise, it creates it from the module and class name

Models also support dict-like access:

len(m)

Returns the number of columns defined in the model

m[col_name]

Returns the value of column col_name

m[col_name] = value

Set m[col_name] to value

keys()

Returns a list of column IDs.

values()

Returns list of column values.

items()

Returns a list of column ID/value tuples.