Introduce deletion-mode for assets

[nicoloboschi]

Same of #418 but for assets.

new field deletion-mode: none|delete. Default is none

When deletion-mode=delete, the delete-statements field is required (list[] string) and all the statements are executed at deletion time.

assets:
- name: "vsearch-keyspace"
    asset-type: "cassandra-keyspace"
    creation-mode: create-if-not-exists
    deletion-mode: delete
    config:
      keyspace: "vsearch"
      datasource: "CassandraDatasource"
      create-statements:
        - "CREATE KEYSPACE vsearch WITH REPLICATION = {'class' : 'SimpleStrategy','replication_factor' : 1};"
      delete-statements:
        - "DROP KEYSPACE vsearch"

[eolivelli]

I don't think this is a good idea, the table may have other dependencies like INDEXes it really depends on how you created it (and we have no control over the create-statements)

if there is no statement then we do nothing, like for create-statements

[nicoloboschi]

it's not very intuitive.
You set deletion-mode: delete and then you have to provide the keyspace delete statement ?
It's much easier if you just delete it.

From my testing, the keyspace is being deleted even if not empty and it works well.

Do you think an INDEX would make the keyspace deletion fail ?

[eolivelli]

also here

[eolivelli]

if the auto delete command works with tables with indexed (for instance of Vector columns) then I am +1

as an alternative we can fail the deployment here

langstream/langstream-core/src/main/java/ai/langstream/impl/assets/CassandraAssetsProvider.java

Line 30 in 965c78e

public class CassandraAssetsProvider extends AbstractAssetProvider {

in any case we must add the validation in CassandraAssetsProvider