Fix constructor deserialization of NumericalTarget (#740)

Fixes #739 by adjusting the deserialization hooks.

Author: AdrianSosic

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+### Fixed
+- Deserialization of `NumericalTarget` objects using the optional `constructor` field
+
 ## [0.14.2] - 2026-01-14
 ### Added
 - `NumericalTarget.match_*` constructors now accept a `mismatch_instead` argument. If 

baybe/serialization/core.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import base64
+import contextlib
 import pickle
 from datetime import datetime, timedelta
 from typing import TYPE_CHECKING, Any, NoReturn, TypeVar, get_type_hints
@@ -129,8 +130,13 @@ def block_deserialization_hook(_: Any, cls: type) -> NoReturn:  # noqa: DOC101,
 def select_constructor_hook(specs: dict, cls: type[_T]) -> _T:
     """Use the constructor specified in the 'constructor' field for deserialization."""
     # If a constructor is specified, use it
-    specs = specs.copy()
     if constructor_name := specs.pop("constructor", None):
+        # Drop potentially existing type field
+        # (The type is already fully determined in this execution branch)
+        specs = specs.copy()
+        specs.pop(_TYPE_FIELD, None)
+
+        # Extract the constructor callable
         constructor = getattr(cls, constructor_name)
 
         # If given a non-attrs class, simply call the constructor
@@ -139,9 +145,14 @@ def select_constructor_hook(specs: dict, cls: type[_T]) -> _T:
 
         # Extract the constructor parameter types and deserialize the arguments
         type_hints = get_type_hints(constructor)
-        for key, value in specs.items():
+        for key in specs:
             annotation = type_hints[key]
-            specs[key] = converter.structure(specs[key], annotation)
+
+            # For some types (e.g. unions), there might not be a registered structure
+            # hook. In this case, the constructor will accept the raw value, so we
+            # simply pass it through.
+            with contextlib.suppress(cattrs.StructureHandlerNotFoundError):
+                specs[key] = converter.structure(specs[key], annotation)
 
         # Call the constructor with the deserialized arguments
         return constructor(**specs)

baybe/targets/numerical.py

@@ -17,7 +17,7 @@
 
 from baybe.exceptions import IncompatibilityError
 from baybe.serialization import SerialMixin, converter
-from baybe.serialization.core import select_constructor_hook
+from baybe.serialization.core import _TYPE_FIELD, select_constructor_hook
 from baybe.targets._deprecated import (
     _VALID_TRANSFORMATIONS,
     TargetMode,
@@ -765,12 +765,16 @@ def summary(self):
         )
 
 
+# Collect leftover original slotted classes processed by `attrs.define`
+gc.collect()
+
 converter.register_unstructure_hook(
     NumericalTarget,
     cattrs.gen.make_dict_unstructure_fn(
         NumericalTarget, converter, _constructor_info=cattrs.override(omit=False)
     ),
 )
+converter.register_structure_hook(NumericalTarget, select_constructor_hook)
 
 
 # >>> Deprecation >>> #
@@ -779,26 +783,11 @@ def summary(self):
 
 
 @converter.register_structure_hook
-def _(dct, cls) -> NumericalTarget:
+def _enable_legacy_target_deserialization(dct: dict[str, Any], cls) -> NumericalTarget:
     if "mode" in dct:
-        return _hook(*dct)
-    return select_constructor_hook(dct, cls)
-
-
-_hook = converter.get_structure_hook(NumericalTarget)
-
-
-@converter.register_structure_hook
-def _structure_legacy_target_arguments(x: dict[str, Any], _) -> NumericalTarget:
-    """Accept legacy target argument for backward compatibility."""
-    x.pop("type", None)
-    try:
-        return _hook(x, _)
-    except Exception:
-        return NumericalTarget(**x)  # type: ignore[return-value]
+        dct.pop(_TYPE_FIELD, None)
+        return NumericalTarget(**dct)
+    return _hook(dct, cls)
 
 
 # <<< Deprecation <<< #
-
-
-gc.collect()

tests/test_deprecations.py

@@ -39,6 +39,7 @@
     linear_transform,
     triangular_transform,
 )
+from baybe.targets.base import Target
 from baybe.targets.binary import BinaryTarget
 from baybe.transformations.basic import AffineTransformation
 
@@ -474,3 +475,20 @@ def test_target_transformation(
     if deprecation is not None:
         assert_series_equal(deprecation.transform(series), expected)
     assert_series_equal(modern.transform(series), expected)
+
+
+def test_deserialization_using_constructor():
+    """Deserialization using the 'constructor' field works despite having other
+    deprecation mechanisms in place."""  # noqa
+    config = """
+    {
+        "type": "NumericalTarget",
+        "name": "t_max_bounds",
+        "constructor": "normalized_ramp",
+        "cutoffs": [0, 100]
+    }
+    """
+    t_old = NumericalTarget("t_max_bounds", mode="MAX", bounds=(0, 100))
+    t_new = NumericalTarget.normalized_ramp("t_max_bounds", cutoffs=(0, 100))
+    t_new_config = Target.from_json(config)
+    assert t_old == t_new == t_new_config