Fix remaining SQLAlchemy 1.4/2.1 doc references and fact-check migration

airflow-core/src/airflow/config_templates/config.yml

@@ -683,7 +683,7 @@ database:
         Check connection at the start of each connection pool checkout.
         Typically, this is a simple statement like "SELECT 1".
         See `SQLAlchemy Pooling: Disconnect Handling - Pessimistic
-        <https://docs.sqlalchemy.org/en/14/core/pooling.html#disconnect-handling-pessimistic>`__
+        <https://docs.sqlalchemy.org/en/20/core/pooling.html#disconnect-handling-pessimistic>`__
         for more details.
       version_added: 2.3.0
       type: boolean

airflow-core/src/airflow/utils/db.py

@@ -90,8 +90,10 @@
     from airflow.models.connection import Connection
     from airflow.typing_compat import Self
 
-    # TODO: Import this from sqlalchemy.orm instead when switching to SQLA 2.
-    # https://docs.sqlalchemy.org/en/20/orm/mapping_api.html#sqlalchemy.orm.MappedClassProtocol
+    # Note: SQLAlchemy 2.x (already required by this package) ships its own
+    # sqlalchemy.orm.MappedClassProtocol, but it checks for __table__/__mapper__/__call__
+    # rather than __tablename__, so it isn't a drop-in replacement for this local protocol.
+    # See https://docs.sqlalchemy.org/en/20/orm/mapping_api.html#sqlalchemy.orm.MappedClassProtocol
     class MappedClassProtocol(Protocol):
         """Protocol for SQLALchemy model base."""
 

airflow-core/tests/unit/utils/test_orm_event_handlers.py

@@ -17,7 +17,7 @@
 
 """
 These tests ensure compatibility with the deprecation of `sqlalchemy.orm.mapper()` in SQLAlchemy 2.0.0.b1.
-See also: https://docs.sqlalchemy.org/en/21/orm/mapping_styles.html#orm-imperative-mapping
+See also: https://docs.sqlalchemy.org/en/20/orm/mapping_styles.html#orm-imperative-mapping
 """
 
 from __future__ import annotations