Allow SQAArm.generator_run_id to be nullable (#4363)

Summary:

**Goal of this stack: attach all arms on the experiment, to the experiment object itself, as the main "ground truth" for them.**

Differential Revision: D83488268

Author: Lena Kashtelyan

ax/storage/sqa_store/sqa_classes.py

@@ -164,8 +164,8 @@ class SQAMetric(Base):
 class SQAArm(Base):
     __tablename__: str = "arm_v2"
 
-    generator_run_id: Column[int] = Column(
-        Integer, ForeignKey("generator_run_v2.id"), nullable=False
+    generator_run_id: Column[int | None] = Column(
+        Integer, ForeignKey("generator_run_v2.id")
     )
     id: Column[int] = Column(Integer, primary_key=True)
     name: Column[str | None] = Column(String(NAME_OR_TYPE_FIELD_LENGTH))

ax/storage/sqa_store/validation.py

@@ -15,6 +15,7 @@
 from ax.storage.sqa_store.sqa_classes import (
     ONLY_ONE_FIELDS,
     ONLY_ONE_METRIC_FIELDS,
+    SQAArm,
     SQAMetric,
     SQAParameter,
     SQAParameterConstraint,
@@ -51,7 +52,6 @@ def wrapper(fn: Callable) -> Callable:
     return wrapper
 
 
-# pyre-fixme[3]: Return annotation cannot be `Any`.
 def consistency_exactly_one(instance: SQABase, exactly_one_fields: list[str]) -> Any:
     """Ensure that exactly one of `exactly_one_fields` has a value set."""
     values = [getattr(instance, field) is not None for field in exactly_one_fields]
@@ -62,29 +62,6 @@ def consistency_exactly_one(instance: SQABase, exactly_one_fields: list[str]) ->
         )
 
 
-@listens_for_multiple(
-    targets=GR_LARGE_MODEL_ATTRS,
-    identifier="set",
-    # `retval=True` instruct the operation ('set' on attributes in `targets`) to use
-    # the return value of decorated function to set the attribute.
-    retval=True,
-    # `propagate=True` ensures that targets with subclasses of SQA classes used by
-    # default Ax OSS encoder inherit the event listeners.
-    propagate=True,
-)
-def do_not_set_existing_value_to_null(
-    instance: SQABase, new_value: T, old_value: T, initiator_event: event.Events
-) -> T:
-    no_value = [None, NO_VALUE]
-    if new_value in no_value and old_value not in no_value:
-        logger.debug(
-            f"New value for attribute is `None` or has no value, but old value "
-            f"was set, so keeping the old value ({old_value})."
-        )
-        return old_value
-    return new_value
-
-
 @event.listens_for(
     SQAParameter,
     "before_insert",
@@ -116,3 +93,26 @@ def validate_metric(mapper: Mapper, connection: Connection, target: SQABase) ->
 @event.listens_for(SQARunner, "before_update")
 def validate_runner(mapper: Mapper, connection: Connection, target: SQABase) -> None:
     consistency_exactly_one(target, ["experiment_id", "trial_id"])
+
+
+@listens_for_multiple(
+    targets=GR_LARGE_MODEL_ATTRS,
+    identifier="set",
+    # `retval=True` instruct the operation ('set' on attributes in `targets`) to use
+    # the return value of decorated function to set the attribute.
+    retval=True,
+    # `propagate=True` ensures that targets with subclasses of SQA classes used by
+    # default Ax OSS encoder inherit the event listeners.
+    propagate=True,
+)
+def do_not_set_existing_value_to_null(
+    instance: SQABase, new_value: T, old_value: T, initiator_event: event.Events
+) -> T:
+    no_value = [None, NO_VALUE]
+    if new_value in no_value and old_value not in no_value:
+        logger.debug(
+            f"New value for attribute is `None` or has no value, but old value "
+            f"was set, so keeping the old value ({old_value})."
+        )
+        return old_value
+    return new_value