CODEWITHSUNDEEP
python-3.xcassandraobject-object-mappingcassandra-4.0datastax-python-driver
Chameleon
Chameleon

Reputation: 10138

How can I create a record with the CQL NOW() function for a columns.UUID?

I want to create some record with Cassandra now() to keep unique identifiers (generation uuid is not good since can be duplicate).

How can I do it using object mapper.

I wrote such model:

class OwnerUnique(models.Model):
    __keyspace__ = 'training'
    __table_name__ = 'owner_unique'

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

I try to use OwnerUnique.create(owner_id='now()') and owner_id = columns.UUID(deafult='now()').

Finnally I gave up and wrote raw query code - whatever maybe it is not need to write this code. I think that setting UUID from now is normal practice so we do not need such flow. How to do it in object mapper?

    @classmethod
    def create_unique_async(cls, name: str) -> ResponseFuture:
        query = '''
insert into training.owner_unique
    (name, owner_id) 
    values (?, now())
    if not exists'''

        params = {
            'name': name
        }

        current_connection: Connection = connection.get_connection('training')
        session = current_connection.session
        prepared_statement = cls._prepared_statements.get(query)
        if prepared_statement is None:
            prepared_statement: PreparedStatement = session.prepare(query)
            cls._prepared_statements[query] = prepared_statement

        response_future: ResponseFuture = session.execute_async(prepared_statement, params)

        return response_future

    @classmethod
    def create_unique(cls, name: str) -> ResultSet:
        response_future = cls.create_unique_async(name)
        result_set = response_future.result()

        return result_set

Upvotes: 0

Views: 33

Answers (2)

absurdfarce
absurdfarce

Reputation: 261

As usual @erick-ramirez has it exactly right. As discussed in the docs for the Python driver the "uuid" CQL type is mapped to the uuid.UUID Python type. Anything which generates a UUID (including the uuid4() method referenced by Erick above) should do the trick.

Upvotes: 1

Erick Ramirez
Erick Ramirez

Reputation: 16373

The UUID module does not have a now() method unlike DateTime which has datetime.now() (returns the local date and time). Still, it is not the same as the CQL function NOW() which generates a time UUID which contains the current timestamp.

Try using the uuid4() method instead to generate a unique ID with default=uuid.uuid4(). Cheers!

Upvotes: 0

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