Fix log task instance join

airflow-core/src/airflow/models/log.py

@@ -28,6 +28,7 @@
 from airflow.utils.sqlalchemy import UtcDateTime, mapped_column
 
 if TYPE_CHECKING:
+    from airflow.models.dag import DagModel
     from airflow.models.taskinstance import TaskInstance
     from airflow.models.taskinstancekey import TaskInstanceKey
 
@@ -50,18 +51,18 @@ class Log(Base):
     extra: Mapped[str | None] = mapped_column(Text, nullable=True)
     try_number: Mapped[int | None] = mapped_column(Integer, nullable=True)
 
-    dag_model = relationship(
+    dag_model: Mapped[DagModel | None] = relationship(
         "DagModel",
         viewonly=True,
         foreign_keys=[dag_id],
         primaryjoin="Log.dag_id == DagModel.dag_id",
     )
 
-    task_instance = relationship(
+    task_instance: Mapped[TaskInstance | None] = relationship(
         "TaskInstance",
         viewonly=True,
-        foreign_keys=[task_id],
-        primaryjoin="Log.task_id == TaskInstance.task_id",
+        foreign_keys=[dag_id, task_id, run_id, map_index],
+        primaryjoin="and_(Log.dag_id == TaskInstance.dag_id, Log.task_id == TaskInstance.task_id, Log.run_id == TaskInstance.run_id, Log.map_index == TaskInstance.map_index)",
         lazy="noload",
     )
 

airflow-core/tests/unit/models/test_log.py

@@ -0,0 +1,84 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from __future__ import annotations
+
+import pytest
+from sqlalchemy import select
+from sqlalchemy.orm import joinedload
+
+from airflow.models.log import Log
+from airflow.operators.empty import EmptyOperator
+from airflow.utils.state import TaskInstanceState
+
+pytestmark = pytest.mark.db_test
+
+
+class TestLogTaskInstanceReproduction:
+    def test_log_task_instance_join_correctness(self, dag_maker, session):
+        # Create dag_1 with a task
+        with dag_maker("dag_1", session=session):
+            EmptyOperator(task_id="common_task_id")
+
+        dr1 = dag_maker.create_dagrun()
+        ti1 = dr1.get_task_instance("common_task_id")
+        ti1.state = TaskInstanceState.SUCCESS
+        session.merge(ti1)
+        session.commit()
+
+        # Create dag_2 with the SAME task_id
+        with dag_maker("dag_2", session=session):
+            EmptyOperator(task_id="common_task_id")
+
+        dr2 = dag_maker.create_dagrun()
+        ti2 = dr2.get_task_instance("common_task_id")
+        ti2.state = TaskInstanceState.FAILED
+        session.merge(ti2)
+        session.commit()
+
+        # Create a log entry specifically for dag_1's task instance
+        log = Log(
+            event="test_event",
+            task_instance=ti1,
+        )
+        session.add(log)
+        session.commit()
+
+        # Query with joinedload to trigger the relationship join
+
+        stmt = select(Log).where(Log.id == log.id).options(joinedload(Log.task_instance))
+        loaded_log = session.scalar(stmt)
+
+        assert loaded_log.task_instance is not None
+        assert loaded_log.task_instance.dag_id == "dag_1"
+        assert loaded_log.task_instance.run_id == ti1.run_id
+
+        # Verify incorrect join for second dag
+        log2 = Log(
+            event="test_event_2",
+            task_instance=ti2,
+        )
+        session.add(log2)
+        session.commit()
+
+        stmt2 = select(Log).where(Log.id == log2.id).options(joinedload(Log.task_instance))
+        loaded_log2 = session.scalar(stmt2)
+
+        # This should fail if the join is ambiguous and picks the first one (dag_1)
+        assert loaded_log2.task_instance is not None
+        assert loaded_log2.task_instance.dag_id == "dag_2"
+        assert loaded_log2.task_instance.run_id == ti2.run_id