fix(model): Disallow creating objects through DeepProxyAccessor

By inheriting from DirectProxyAccessor, DeepProxyAccessor also
unintentionally inherited the behaviors that allowed creating objects.
This recently led to confusion as to what's possible and what isn't.

Part of the fix to #446.

capellambse/model/_descriptors.py

@@ -814,18 +814,94 @@ def purge_references(
         yield
 
 
-class DeepProxyAccessor(DirectProxyAccessor[T]):
+class DeepProxyAccessor(PhysicalAccessor[T]):
     """A DirectProxyAccessor that searches recursively through the tree."""
 
     __slots__ = ()
 
+    def __init__(
+        self,
+        class_: type[T],
+        xtypes: str | type[T] | cabc.Iterable[str | type[T]] | None = None,
+        *,
+        aslist: type[_obj.ElementList] | None = None,
+        rootelem: (
+            type[_obj.GenericElement]
+            | cabc.Sequence[type[_obj.GenericElement]]
+            | None
+        ) = None,
+    ) -> None:
+        """Create a DeepProxyAccessor.
+
+        Parameters
+        ----------
+        class_
+            The proxy class.
+        xtypes
+            The ``xsi:type`` (or types) to search for. If None, defaults
+            to the type of the passed ``class_``.
+        aslist
+            A subclass of :class:`~capellambse.model.ElementList` to use
+            for returning a list of all matched objects. If not
+            specified, defaults to the base ElementList.
+        rootelem
+            Limit the search scope to objects of this type, nested below
+            the current object. When passing a sequence, defines a path
+            of object types to follow.
+        """
+        if aslist is None:
+            aslist = _obj.ElementList
+        super().__init__(
+            class_,
+            xtypes,
+            aslist=aslist,
+        )
+        if rootelem is None:
+            self.rootelem: cabc.Sequence[str] = ()
+        elif isinstance(rootelem, type) and issubclass(
+            rootelem, _obj.GenericElement
+        ):
+            self.rootelem = (_xtype.build_xtype(rootelem),)
+        elif not isinstance(rootelem, str):  # type: ignore[unreachable]
+            self.rootelem = tuple(_xtype.build_xtype(i) for i in rootelem)
+        else:
+            raise TypeError(
+                "Invalid 'rootelem', expected a type or list of types: "
+                + repr(rootelem)
+            )
+
+    @t.overload
+    def __get__(self, obj: None, objtype: type[t.Any]) -> te.Self: ...
+    @t.overload
+    def __get__(
+        self, obj: _obj.ModelObject, objtype: type[t.Any] | None = ...
+    ) -> _obj.ElementList[T]: ...
+    def __get__(
+        self,
+        obj: _obj.ModelObject | None,
+        objtype: type[t.Any] | None = None,
+    ) -> te.Self | _obj.ElementList[T]:
+        del objtype
+        if obj is None:  # pragma: no cover
+            return self
+
+        elems = [e for e in self._getsubelems(obj) if e.get("id") is not None]
+        assert self.aslist is not None
+        return self.aslist(obj._model, elems)
+
     def _getsubelems(
         self, obj: _obj.ModelObject
     ) -> cabc.Iterator[etree._Element]:
-        return itertools.chain.from_iterable(
-            obj._model._loader.iterdescendants_xt(i, *iter(self.xtypes))
-            for i in self._findroots(obj)
-        )
+        ldr = obj._model._loader
+        roots = [obj._element]
+        for xtype in self.rootelem:
+            roots = list(
+                itertools.chain.from_iterable(
+                    ldr.iterchildren_xt(i, xtype) for i in roots
+                )
+            )
+        for root in roots:
+            yield from ldr.iterdescendants_xt(root, *self.xtypes)
 
 
 class LinkAccessor(WritableAccessor[T], PhysicalAccessor[T]):

tests/test_metamodel_cs.py

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 from capellambse import MelodyModel
+from capellambse.metamodel import cs
 
 
 def test_PhysicalPath_has_ordered_list_of_involved_items(model: MelodyModel):
@@ -51,6 +52,7 @@ def test_PhysicalLink_has_exchanges(model: MelodyModel):
 
 def test_PhysicalLink_setting_ends(model: MelodyModel):
     link = model.pa.all_physical_links.by_name("Eth Cable 2")
+    assert isinstance(link, cs.PhysicalLink)
     source_pp = model.by_uuid("76d9c301-c0ad-4615-9f02-b804b018decf")
     target_pp = model.by_uuid("53c9fe29-18e2-4642-906e-b7507bf0ff39")
 
@@ -64,6 +66,7 @@ def test_PhysicalLink_setting_ends(model: MelodyModel):
 
 def test_PhysicalLink_setting_source_and_target(model: MelodyModel):
     link = model.pa.all_physical_links.by_name("Eth Cable 2")
+    assert isinstance(link, cs.PhysicalLink)
     source_pp = model.by_uuid("76d9c301-c0ad-4615-9f02-b804b018decf")
     target_pp = model.by_uuid("53c9fe29-18e2-4642-906e-b7507bf0ff39")
 

tests/test_model_layers.py

@@ -137,12 +137,13 @@ def test_ElementList_dictlike_setitem(model: m.MelodyModel):
 
 
 def test_MixedElementList_filter_by_type(model: m.MelodyModel):
-    process = model.oa.all_processes.by_uuid(
-        "d588e41f-ec4d-4fa9-ad6d-056868c66274"
-    )
+    process = model.by_uuid("d588e41f-ec4d-4fa9-ad6d-056868c66274")
+    assert isinstance(process, mm.oa.OperationalProcess)
+
     involvements = process.involved
     acts = involvements.by_type("OperationalActivity")
     fexs = involvements.by_type("FunctionalExchange")
+
     assert len(involvements) == 7
     assert len(acts) == 4
     assert len(fexs) == 3
@@ -169,6 +170,7 @@ def test_GenericElement_attrs(model: m.MelodyModel, key: str, value: str):
 
 def test_GenericElement_has_diagrams(model: m.MelodyModel):
     elm = model.oa.all_capabilities.by_name("Eat food")
+    assert isinstance(elm, mm.oa.OperationalCapability)
     assert hasattr(elm, "diagrams")
     assert len(elm.diagrams) == 0
 
@@ -186,6 +188,7 @@ def test_GenericElement_has_progress_status(model: m.MelodyModel):
 
 def test_Capabilities_have_constraints(model: m.MelodyModel):
     elm = model.oa.all_capabilities.by_name("Eat food")
+    assert isinstance(elm, mm.oa.OperationalCapability)
     assert hasattr(elm, "constraints")
     assert len(elm.constraints) == 3
 
@@ -337,27 +340,24 @@ def test_stm_accessible_from_component_pkg(self, model: m.MelodyModel):
 
     def test_stm_has_regions(self, model: m.MelodyModel):
         entity = model.oa.all_entities.by_name("Functional Human Being")
+        assert isinstance(entity, mm.oa.Entity)
         state_machine = entity.state_machines[0]
 
         assert hasattr(state_machine, "regions")
         assert len(state_machine.regions) == 1
 
     def test_stm_region(self, model: m.MelodyModel):
         entity = model.oa.all_entities.by_name("Functional Human Being")
+        assert isinstance(entity, mm.oa.Entity)
         region = entity.state_machines[0].regions[0]
 
         assert len(region.states) == 12
         assert len(region.modes) == 0
         assert len(region.transitions) == 14
 
     def test_stm_state_mode_regions_well_defined(self, model: m.MelodyModel):
-        mode = (
-            model.oa.all_entities.by_name("Environment")
-            .entities.by_name("Weather")
-            .state_machines[0]
-            .regions[0]
-            .modes.by_name("Day")
-        )
+        mode = model.by_uuid("91dc2eec-c878-4fdb-91d8-8f4a4527424e")
+        assert isinstance(mode, mm.capellacommon.Mode)
 
         assert hasattr(mode, "regions")
         assert len(mode.regions) == 1
@@ -366,12 +366,8 @@ def test_stm_state_mode_regions_well_defined(self, model: m.MelodyModel):
     def test_stm_transition_attributes_well_defined(
         self, model: m.MelodyModel
     ):
-        transition = (
-            model.oa.all_entities.by_name("Functional Human Being")
-            .state_machines[0]
-            .regions[0]
-            .transitions.by_uuid("a78cf778-0476-4e08-a3a3-c115dca55dd1")
-        )
+        transition = model.by_uuid("a78cf778-0476-4e08-a3a3-c115dca55dd1")
+        assert isinstance(transition, mm.capellacommon.StateTransition)
 
         assert hasattr(transition, "source")
         assert transition.source is not None
@@ -423,11 +419,6 @@ def test_stm_region_has_access_to_diagrams(self, model: m.MelodyModel):
         assert sleep_region.diagrams
         assert sleep_region.diagrams[0].name == "[MSM] Keep the sleep schedule"
 
-    def test_stm_state_has_functions(self, model: m.MelodyModel):
-        state = model.by_uuid("957c5799-1d4a-4ac0-b5de-33a65bf1519c")
-        assert len(state.functions) == 4  # leaf functions only
-        assert "teach Care of Magical Creatures" in state.functions.by_name
-
 
 def test_exchange_items_of_a_function_port(model: m.MelodyModel):
     port = model.by_uuid("db64f0c9-ea1c-4962-b043-1774547c36f7")