pgvector - hnsw index table drop is not using schema name

[mabartcz]

Describe the bug
If using pgvector, hnsw and multiple schema names (not the default one) the "hnsw index drop" does not drop the table, even if
hnsw_recreate_index_if_exists=True.

It seems to me that there is missing schema_name before table_name in drop index SQL query in:
pgvector/document_store.py (row 392)

Current code:
sql_drop_index = SQL("DROP INDEX IF EXISTS {index_name}").format(index_name=Identifier(self.hnsw_index_name))

Should be:
sql_drop_index = SQL("DROP INDEX IF EXISTS {schema_name}.{index_name}").format(schema_name=Identifier(self.schema_name),index_name=Identifier(self.hnsw_index_name))

To Reproduce

1. Create PostgreSQL with pgvector using docker (pgvector/pgvector:pg17)
2. Try to write documents 2 times with same table name (hnsw index should be dropped but it is not.
   Minimal example code: https://gist.github.com/mabartcz/4faa3e1ae7a56c8a9536b1ab8e7d4572
3. Get error: "psycopg.errors.DuplicateTable: relation "test_table_index" already exists"

Describe your environment (please complete the following information):

• OS: Windows 11
• pgvector-haystack: 1.2.0
• haystack-ai: 2.8.0

If I am not missing something, I can create PR to fix the issue :)

[anakin87]

Hello and thank you for reporting the issue.

I think you are right.

Would you like to open a PR to fix this bug (and add a small test)?
(Contributing guidelines)

[mabartcz]

Yes, I will open PR with fix and test.