Function to expand mapped tasks in to multiple "real" TIs

airflow/models/baseoperator.py

@@ -75,6 +75,7 @@
 from airflow.utils.log.logging_mixin import LoggingMixin
 from airflow.utils.operator_resources import Resources
 from airflow.utils.session import NEW_SESSION, provide_session
+from airflow.utils.state import State, TaskInstanceState
 from airflow.utils.trigger_rule import TriggerRule
 from airflow.utils.weight_rule import WeightRule
 
@@ -1800,6 +1801,73 @@ def wait_for_downstream(self) -> bool:
     def depends_on_past(self) -> bool:
         return self.partial_kwargs.get("depends_on_past") or self.wait_for_downstream
 
+    def expand_mapped_task(self, upstream_ti: "TaskInstance", session: "Session" = NEW_SESSION) -> None:
+        """Create the mapped TaskInstances for mapped task."""
+        # TODO: support having multiuple mapped upstreams?
+        from airflow.models.taskmap import TaskMap
+        from airflow.settings import task_instance_mutation_hook
+
+        task_map_info_length: Optional[int] = (
+            session.query(TaskMap.length)
+            .filter_by(
+                dag_id=upstream_ti.dag_id,
+                task_id=upstream_ti.task_id,
+                run_id=upstream_ti.run_id,
+                map_index=upstream_ti.map_index,
+            )
+            .scalar()
+        )
+        if task_map_info_length is None:
+            # TODO: What would lead to this? How can this be better handled?
+            raise RuntimeError("mapped operator cannot be expanded; upstream not found")
+        # TODO: Add db constraint to ensure this is never negative.
+
+        unmapped_ti: Optional[TaskInstance] = (
+            session.query(TaskInstance)
+            .filter(
+                TaskInstance.dag_id == upstream_ti.dag_id,
+                TaskInstance.run_id == upstream_ti.run_id,
+                TaskInstance.task_id == self.task_id,
+                TaskInstance.map_index == -1,
+                TaskInstance.state.in_(State.unfinished),
+            )
+            .one_or_none()
+        )
+
+        if unmapped_ti:
+            # The unmapped task instance still exists and is unfinished, i.e. we
+            # haven't tried to run it before.
+            if task_map_info_length < 1:
+                # If the upstream maps this to a zero-length value, simply marked the
+                # unmapped task instance as SKIPPED (if needed).
+                unmapped_ti.state = TaskInstanceState.SKIPPED
+                session.merge(unmapped_ti)
+                return
+            # Otherwise convert this into the first mapped index, and create
+            # TaskInstance for other indexes.
+            unmapped_ti.map_index = 0
+            indexes_to_map = range(1, task_map_info_length)
+        else:
+            indexes_to_map = range(task_map_info_length)
+
+        for index in indexes_to_map:
+            # TODO: Make more efficient with bulk_insert_mappings/bulk_save_mappings.
+            # TODO: Change `TaskInstance` ctor to take Operator, not BaseOperator
+            ti = TaskInstance(self, run_id=upstream_ti.run_id, map_index=index)  # type: ignore
+            task_instance_mutation_hook(ti)
+            session.merge(ti)
+
+        # Set to "REMOVED" any (old) TaskInstances with map indices greater
+        # than the current map value
+        session.query(TaskInstance).filter(
+            TaskInstance.dag_id == upstream_ti.dag_id,
+            TaskInstance.task_id == self.task_id,
+            TaskInstance.run_id == upstream_ti.run_id,
+            TaskInstance.map_index >= task_map_info_length,
+        ).update({TaskInstance.state: TaskInstanceState.REMOVED})
+
+        session.flush()
+
 
 # TODO: Deprecate for Airflow 3.0
 Chainable = Union[DependencyMixin, Sequence[DependencyMixin]]

airflow/models/taskinstance.py

@@ -486,7 +486,7 @@ def __init__(
         self.test_mode = False
 
     @staticmethod
-    def insert_mapping(run_id: str, task: "BaseOperator") -> dict:
+    def insert_mapping(run_id: str, task: "BaseOperator", map_index: int = -1) -> dict:
         """:meta private:"""
         return {
             'dag_id': task.dag_id,
@@ -503,6 +503,7 @@ def insert_mapping(run_id: str, task: "BaseOperator") -> dict:
             'max_tries': task.retries,
             'executor_config': task.executor_config,
             'operator': task.task_type,
+            'map_index': map_index,
         }
 
     @reconstructor

tests/models/test_baseoperator.py

@@ -36,8 +36,12 @@
     chain,
     cross_downstream,
 )
+from airflow.models.taskinstance import TaskInstance
+from airflow.models.taskmap import TaskMap
+from airflow.models.xcom_arg import XComArg
 from airflow.utils.context import Context
 from airflow.utils.edgemodifier import Label
+from airflow.utils.state import TaskInstanceState
 from airflow.utils.task_group import TaskGroup
 from airflow.utils.trigger_rule import TriggerRule
 from airflow.utils.weight_rule import WeightRule
@@ -733,8 +737,6 @@ def test_map_unknown_arg_raises():
 
 def test_map_xcom_arg():
     """Test that dependencies are correct when mapping with an XComArg"""
-    from airflow.models.xcom_arg import XComArg
-
     with DAG("test-dag", start_date=DEFAULT_DATE):
         task1 = BaseOperator(task_id="op1")
         xcomarg = XComArg(task1, "test_key")
@@ -767,3 +769,63 @@ def test_partial_on_class_invalid_ctor_args() -> None:
     """
     with pytest.raises(TypeError, match=r"arguments 'foo', 'bar'"):
         MockOperator.partial(task_id='a', foo='bar', bar=2)
+
+
+@pytest.mark.parametrize(
+    ["num_existing_tis", "expected"],
+    (
+        pytest.param(0, [(0, None), (1, None), (2, None)], id='only-unmapped-ti-exists'),
+        pytest.param(3, [(0, None), (1, None), (2, None)], id='all-tis-exist'),
+        pytest.param(
+            5,
+            [(0, None), (1, None), (2, None), (3, TaskInstanceState.REMOVED), (4, TaskInstanceState.REMOVED)],
+            id="tis-to-be-remove",
+        ),
+    ),
+)
+def test_expand_mapped_task_instance(dag_maker, session, num_existing_tis, expected):
+    literal = [1, 2, {'a': 'b'}]
+    with dag_maker(session=session):
+        task1 = BaseOperator(task_id="op1")
+        xcomarg = XComArg(task1, "test_key")
+        mapped = MockOperator(task_id='task_2').map(arg2=xcomarg)
+
+    dr = dag_maker.create_dagrun()
+
+    session.add(
+        TaskMap(
+            dag_id=dr.dag_id,
+            task_id=task1.task_id,
+            run_id=dr.run_id,
+            map_index=-1,
+            length=len(literal),
+            keys=None,
+        )
+    )
+
+    if num_existing_tis:
+        # Remove the map_index=-1 TI when we're creating other TIs
+        session.query(TaskInstance).filter(
+            TaskInstance.dag_id == mapped.dag_id,
+            TaskInstance.task_id == mapped.task_id,
+            TaskInstance.run_id == dr.run_id,
+        ).delete()
+
+    for index in range(num_existing_tis):
+        ti = TaskInstance(mapped, run_id=dr.run_id, map_index=index)
+        session.add(ti)
+    session.flush()
+
+    mapped.expand_mapped_task(
+        upstream_ti=dr.get_task_instance(task1.task_id),
+        session=session,
+    )
+
+    indices = (
+        session.query(TaskInstance.map_index, TaskInstance.state)
+        .filter_by(task_id=mapped.task_id, dag_id=mapped.dag_id, run_id=dr.run_id)
+        .order_by(TaskInstance.map_index)
+        .all()
+    )
+
+    assert indices == expected

tests/models/test_dagrun.py

@@ -39,6 +39,7 @@
 from airflow.utils.types import DagRunType
 from tests.models import DEFAULT_DATE
 from tests.test_utils.db import clear_db_dags, clear_db_pools, clear_db_runs
+from tests.test_utils.mock_operators import MockOperator
 
 
 class TestDagRun(unittest.TestCase):
@@ -874,3 +875,20 @@ def test_verify_integrity_task_start_date(Stats_incr, session, run_type, expecte
     assert len(tis) == expected_tis
 
     Stats_incr.assert_called_with('task_instance_created-DummyOperator', expected_tis)
+
+
+@pytest.mark.xfail(reason="TODO: Expand mapped literals at verify_integrity time!")
+def test_expand_mapped_task_instance(dag_maker, session):
+    literal = [1, 2, {'a': 'b'}]
+    with dag_maker(session=session):
+        mapped = MockOperator(task_id='task_2').map(arg2=literal)
+
+    dr = dag_maker.create_dagrun()
+    indices = (
+        session.query(TI.map_index)
+        .filter_by(task_id=mapped.task_id, dag_id=mapped.dag_id, run_id=dr.run_id)
+        .order_by(TI.insert_mapping)
+        .all()
+    )
+
+    assert indices == [0, 1, 2]