Python loop inserting last row only in cassandra

Question

I typed a small demo loop in order to insert random values in Cassandra but only the last record is persisted into the database. I am using cassandra-driver from datastax and its object modeling lib. Cassandra version is 3.7 and Python 3.4. Any idea what I am doing wrong?

#!/usr/bin/env python

import datetime
import uuid
from random import randint, uniform
from cassandra.cluster import Cluster
from cassandra.cqlengine import connection, columns
from cassandra.cqlengine.management import sync_table
from cassandra.cqlengine.models import Model
from cassandra.cqlengine.query import BatchQuery

class TestTable(Model):
    _table_name = 'test_table'
    key = columns.UUID(primary_key=True, default=uuid.uuid4())
    type = columns.Integer(index=True)
    value = columns.Float(required=False)
    created_time = columns.DateTime(default=datetime.datetime.now())


def main():
    connection.setup(['127.0.0.1'], 'test', protocol_version = 3)
    sync_table(TestTable)

    for _ in range(10):
        type = randint(1, 3)
        value = uniform(-10, 10)
        row = TestTable.create(type=type, value=value)
        print("Inserted row: ", row.type, row.value)

    print("Done inserting")

    q = TestTable.objects.count()
    print("We have inserted " + str(q) + " rows.")


if __name__ == "__main__":
    main()

Many thanks!

BrianC · Accepted Answer · 2016-08-22 03:59:13Z

2

The problem is in the definition of the key column:

key = columns.UUID(primary_key=True, default=uuid.uuid4())

For the default value it's going to call the uuid.uuid4 function once and use that result as the default for all future inserts. Because that's your primary key, all 10 writes will happen to the same primary key.

Instead, drop the parentheses so you are just passing a reference to uuid.uuid4 rather than calling it:

key = columns.UUID(primary_key=True, default=uuid.uuid4)

Now each time you create a row you'll get a new unique UUID value, and therefore a new row in Cassandra.

edited Aug 22, 2016 at 3:59

answered Aug 15, 2016 at 21:51

BrianC

10.7k2 gold badges35 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Leonardo Andrade · Accepted Answer · 2016-08-15 11:46:11Z

0

You need to use the method save.

...
row = TestTable(type=type, value=value)
row.save()
...

http://cqlengine.readthedocs.io/en/latest/topics/models.html#cqlengine.models.Model.save

answered Aug 15, 2016 at 11:46

Leonardo Andrade

6165 silver badges9 bronze badges

1 Comment

user3159821 Over a year ago

Thanks but it keeps failing. It is weird as if I write these two lines twice, only one record is stored too.

Collectives™ on Stack Overflow

Python loop inserting last row only in cassandra

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related