1fanwang commented on code in PR #50677:
URL: https://github.com/apache/airflow/pull/50677#discussion_r2098543605


##########
airflow-core/src/airflow/models/deadline.py:
##########
@@ -123,7 +122,71 @@ class DeadlineReference(Enum):
     dag.deadline.reference.evaluate_with(dag_id=dag.dag_id)
     """
 
+    # Available References.
+    #
+    # The value is the name of the method executed to fetch the datetime
+    # value for the given Reference. For example DAGRUN_LOGICAL_DATE = 
"dagrun_logical_date"
+    # will execute dagrun_logical_date() to find the dagrun's logical date.
     DAGRUN_LOGICAL_DATE = "dagrun_logical_date"
+    DAGRUN_QUEUED_AT = "dagrun_queued_at"
+    _CUSTOM_REFERENCE_BASE = "_custom_reference"
+
+    def __init__(self, value):
+        self._fixed_dt = None  # Initialize the storage for fixed datetime
+        super().__init__()
+
+    @classmethod
+    def FIXED_DATETIME(cls, dt: datetime):
+        """
+        Calculate a reference based on a set datetime rather than fetching a 
value from the database.
+
+        For example, you could set the Deadline for "tomorrow before 9AM" by
+        providing the appropriate datetime object."
+        """
+        instance = object.__new__(cls)
+        instance._value_ = "fixed_datetime"
+        instance._fixed_dt = dt
+        return instance
+
+    def evaluate_with(self, **kwargs):
+        """Call the method in the enum's value with the provided kwargs."""
+        if self._fixed_dt:
+            return self._fixed_dt
+        return getattr(self, self.value)(**kwargs)
+
+    def evaluate(self):
+        """Call evaluate_with() without any conditions, because it looks 
strange in use that way."""
+        return self.evaluate_with()
+
+    @provide_session
+    def _fetch_from_db(self, model_class: Base, column: str, session=None, 
**conditions) -> datetime:

Review Comment:
   no strong opinion on this
   makes sense if we expect to be reusing this



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