Don't show stale Serialized DAGs if they are deleted in DB

airflow/models/dagbag.py

@@ -190,6 +190,8 @@ def get_dag(self, dag_id, session: Session = None):
             # 1. if time has come to check if DAG is updated (controlled by min_serialized_dag_fetch_secs)
             # 2. check the last_updated column in SerializedDag table to see if Serialized DAG is updated
             # 3. if (2) is yes, fetch the Serialized DAG.
+            # 4. if (2) returns None (i.e. Serialized DAG is deleted), remove dag from dagbag
+            # if it exists and return None.
             min_serialized_dag_fetch_secs = timedelta(seconds=settings.MIN_SERIALIZED_DAG_FETCH_INTERVAL)
             if (
                 dag_id in self.dags_last_fetched
@@ -199,7 +201,14 @@ def get_dag(self, dag_id, session: Session = None):
                     dag_id=dag_id,
                     session=session,
                 )
-                if sd_last_updated_datetime and sd_last_updated_datetime > self.dags_last_fetched[dag_id]:
+                if not sd_last_updated_datetime:
+                    self.log.warning("Serialized DAG %s no longer exists", dag_id)
+                    del self.dags[dag_id]
+                    del self.dags_last_fetched[dag_id]
+                    del self.dags_hash[dag_id]
+                    return None
+
+                if sd_last_updated_datetime > self.dags_last_fetched[dag_id]:
                     self._add_dag_from_db(dag_id=dag_id, session=session)
 
             return self.dags.get(dag_id)

airflow/models/serialized_dag.py

@@ -266,7 +266,7 @@ def bulk_sync_to_db(dags: List[DAG], session: Session = None):
 
     @classmethod
     @provide_session
-    def get_last_updated_datetime(cls, dag_id: str, session: Session = None) -> datetime:
+    def get_last_updated_datetime(cls, dag_id: str, session: Session = None) -> Optional[datetime]:
         """
         Get the date when the Serialized DAG associated to DAG was last updated
         in serialized_dag table
@@ -300,7 +300,7 @@ def get_latest_version_hash(cls, dag_id: str, session: Session = None) -> str:
         :param session: ORM Session
         :type session: Session
         :return: DAG Hash
-        :rtype: str
+        :rtype: str | None
         """
         return session.query(cls.dag_hash).filter(cls.dag_id == dag_id).scalar()
 

tests/models/test_dagbag.py

@@ -19,7 +19,7 @@
 import shutil
 import textwrap
 import unittest
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 from tempfile import NamedTemporaryFile, mkdtemp
 from unittest import mock
 from unittest.mock import patch
@@ -33,6 +33,7 @@
 from airflow.exceptions import SerializationError
 from airflow.models import DagBag, DagModel
 from airflow.models.serialized_dag import SerializedDagModel
+from airflow.serialization.serialized_objects import SerializedDAG
 from airflow.utils.dates import timezone as tz
 from airflow.utils.session import create_session
 from airflow.www.security import ApplessAirflowSecurityManager
@@ -311,6 +312,34 @@ def process_file(self, filepath, only_if_updated=True, safe_mode=True):
         assert dag_id == dag.dag_id
         assert 2 == dagbag.process_file_calls
 
+    def test_dag_removed_if_serialized_dag_is_removed(self):
+        """
+        Test that if a DAG does not exist in serialized_dag table (as the DAG file was removed),
+        remove dags from the DagBag
+        """
+        from airflow.operators.dummy import DummyOperator
+
+        dag = models.DAG(
+            dag_id="test_dag_removed_if_serialized_dag_is_removed",
+            schedule_interval=None,
+            start_date=tz.datetime(2021, 10, 12),
+        )
+
+        with dag:
+            DummyOperator(task_id="task_1")
+
+        dagbag = DagBag(dag_folder=self.empty_dir, include_examples=False, read_dags_from_db=True)
+        dagbag.dags = {dag.dag_id: SerializedDAG.from_dict(SerializedDAG.to_dict(dag))}
+        dagbag.dags_last_fetched = {dag.dag_id: (tz.utcnow() - timedelta(minutes=2))}
+        dagbag.dags_hash = {dag.dag_id: mock.ANY}
+
+        assert SerializedDagModel.has_dag(dag.dag_id) is False
+
+        assert dagbag.get_dag(dag.dag_id) is None
+        assert dag.dag_id not in dagbag.dags
+        assert dag.dag_id not in dagbag.dags_last_fetched
+        assert dag.dag_id not in dagbag.dags_hash
+
     def process_dag(self, create_dag):
         """
         Helper method to process a file generated from the input create_dag function.