Support frozen collections with FULL indexes in cqlengine

[dkropachev]

Background

Currently, cqlengine only supports non-frozen collection columns with secondary indexes (VALUES indexing). There's no way to create frozen collections with FULL indexes.

Current Behavior

class MyModel(Model):
    id = columns.Integer(primary_key=True)
    items = columns.List(columns.Text, index=True)

Generates:

CREATE TABLE mymodel (id int PRIMARY KEY, items list<text>);
CREATE INDEX ON mymodel (items);  -- VALUES index (implicit)

Desired Feature

Support frozen collections with FULL indexes:

class MyModel(Model):
    id = columns.Integer(primary_key=True)
    items = columns.List(columns.Text, frozen=True, index=True)

Should generate:

CREATE TABLE mymodel (id int PRIMARY KEY, items frozen<list<text>>);
CREATE INDEX ON mymodel (FULL(items));

Query Behavior Differences

Collection Type	Index Type	Supported Queries
Non-frozen list	VALUES (implicit)	WHERE items CONTAINS 'value'
Frozen list	FULL	WHERE items = ['exact', 'match']

References

• Scylla docs: https://docs.scylladb.com/stable/cql/secondary-indexes.html
• Cassandra docs: https://cassandra.apache.org/doc/latest/cassandra/cql/indexes.html