Ensure compatibility with both SQLAlchemy v1/v2
fix the issue when using SQLAlchemy v1 (reported at #3884)
`
langchain/vectorstores/pgvector.py", line 168, in
create_tables_if_not_exists
self._conn.commit()
AttributeError: 'Connection' object has no attribute 'commit'
`
Ref Doc :
https://docs.sqlalchemy.org/en/14/changelog/migration_20.html#migration-20-autocommit
Related to [this
issue.](https://github.com/hwchase17/langchain/issues/3655#issuecomment-1529415363)
The `Mapped` SQLAlchemy class is introduced in SQLAlchemy 1.4 but the
migration from 1.3 to 1.4 is quite challenging so, IMO, it's better to
keep backwards compatibility and not change the SQLAlchemy requirements
just because of type annotations.
Avoid using placeholder methods that only perform a `cast()`
operation because the typing would otherwise be inferred to be the
parent `VectorStore` class. This is unnecessary with TypeVar's.
The `CollectionStore` for `PGVector` has a `cmetadata` field but it's
never used. This PR add the ability to save metadata information to the
collection.
玄猫