Cassandra CQLEngine无法反映模型架构更改-迁移

Question

I followed the cassandra cqlengine tutorial.

import uuid
from cassandra.cqlengine import columns
from cassandra.cqlengine import connection
from datetime import datetime
from cassandra.cqlengine.management import sync_table
from cassandra.cqlengine.models import Model

class ExampleModel(Model):
    example_id      = columns.UUID(primary_key=True, default=uuid.uuid4)
    example_type    = columns.Integer(index=True)
    created_at      = columns.DateTime()
    description     = columns.Text(required=False)

connection.setup(['127.0.0.1'], "cqlengine", protocol_version=3)
sync_table(ExampleModel)

However when i change a field in the model, like if i change the field description from Text type to Integer type, and then do a sync_table, i dont see the change being reflected in the tables schema in cassandra. How can this be solved ?

Answer 1

There are two things wrong here:

1. Conceptually, you are attempting a schema migration. The apache Cassandra driver for python does not really support schema migration officially yet. A quick look at this ticket will explain to you what I mean. (Note: you could add new column to your table and sync_table will work and your new schema will be reflected but that is not strictly speaking an ALTER operation.)

2. Cassandra data type conversions in a data model must follow the CQL type compatibility, which is defined here . Your attempt to convert from Integer to Float is not compatible.

The only solution so far to update schema with imcompatible types is outlined here . I opened a separate discussion on the same here .