Stop inheriting non-indexed coordinates for DataTree

xarray/core/dataarray.py

@@ -69,7 +69,7 @@
 )
 from xarray.core.utils import (
     Default,
-    HybridMappingProxy,
+    FilteredMapping,
     ReprObject,
     _default,
     either_dict_or_kwargs,
@@ -929,11 +929,10 @@ def _attr_sources(self) -> Iterable[Mapping[Hashable, Any]]:
     @property
     def _item_sources(self) -> Iterable[Mapping[Hashable, Any]]:
         """Places to look-up items for key-completion"""
-        yield HybridMappingProxy(keys=self._coords, mapping=self.coords)
+        yield FilteredMapping(keys=self._coords, mapping=self.coords)
 
         # virtual coordinates
-        # uses empty dict -- everything here can already be found in self.coords.
-        yield HybridMappingProxy(keys=self.dims, mapping={})
+        yield FilteredMapping(keys=self.dims, mapping=self.coords)
 
     def __contains__(self, key: Any) -> bool:
         return key in self.data

xarray/core/dataset.py

@@ -103,9 +103,9 @@
 )
 from xarray.core.utils import (
     Default,
+    FilteredMapping,
     Frozen,
     FrozenMappingWarningOnValuesAccess,
-    HybridMappingProxy,
     OrderedSet,
     _default,
     decode_numpy_dict_values,
@@ -1507,10 +1507,10 @@ def _attr_sources(self) -> Iterable[Mapping[Hashable, Any]]:
     def _item_sources(self) -> Iterable[Mapping[Hashable, Any]]:
         """Places to look-up items for key-completion"""
         yield self.data_vars
-        yield HybridMappingProxy(keys=self._coord_names, mapping=self.coords)
+        yield FilteredMapping(keys=self._coord_names, mapping=self.coords)
 
         # virtual coordinates
-        yield HybridMappingProxy(keys=self.sizes, mapping=self)
+        yield FilteredMapping(keys=self.sizes, mapping=self)
 
     def __contains__(self, key: object) -> bool:
         """The 'in' operator will return true or false depending on whether

xarray/core/datatree.py

@@ -40,8 +40,8 @@
 from xarray.core.treenode import NamedNode, NodePath
 from xarray.core.utils import (
     Default,
+    FilteredMapping,
     Frozen,
-    HybridMappingProxy,
     _default,
     either_dict_or_kwargs,
     maybe_wrap_array,
@@ -516,10 +516,17 @@ def _pre_attach(self: DataTree, parent: DataTree, name: str) -> None:
         check_alignment(path, node_ds, parent_ds, self.children)
         _deduplicate_inherited_coordinates(self, parent)
 
+    @property
+    def _node_coord_variables_with_index(self) -> Mapping[Hashable, Variable]:
+        return FilteredMapping(
+            keys=self._node_indexes, mapping=self._node_coord_variables
+        )
+
     @property
     def _coord_variables(self) -> ChainMap[Hashable, Variable]:
         return ChainMap(
-            self._node_coord_variables, *(p._node_coord_variables for p in self.parents)
+            self._node_coord_variables,
+            *(p._node_coord_variables_with_index for p in self.parents),
         )
 
     @property
@@ -720,10 +727,10 @@ def _attr_sources(self) -> Iterable[Mapping[Hashable, Any]]:
     def _item_sources(self) -> Iterable[Mapping[Any, Any]]:
         """Places to look-up items for key-completion"""
         yield self.data_vars
-        yield HybridMappingProxy(keys=self._coord_variables, mapping=self.coords)
+        yield FilteredMapping(keys=self._coord_variables, mapping=self.coords)
 
         # virtual coordinates
-        yield HybridMappingProxy(keys=self.dims, mapping=self)
+        yield FilteredMapping(keys=self.dims, mapping=self)
 
         # immediate child nodes
         yield self.children

xarray/core/utils.py

@@ -465,33 +465,39 @@ def values(self) -> ValuesView[V]:
         return super().values()
 
 
-class HybridMappingProxy(Mapping[K, V]):
+class FilteredMapping(Mapping[K, V]):
     """Implements the Mapping interface. Uses the wrapped mapping for item lookup
     and a separate wrapped keys collection for iteration.
 
     Can be used to construct a mapping object from another dict-like object without
     eagerly accessing its items or when a mapping object is expected but only
     iteration over keys is actually used.
 
-    Note: HybridMappingProxy does not validate consistency of the provided `keys`
-    and `mapping`. It is the caller's responsibility to ensure that they are
-    suitable for the task at hand.
+    Note: keys should be a subset of mapping, but FilteredMapping does not
+    validate consistency of the provided `keys` and `mapping`. It is the
+    caller's responsibility to ensure that they are suitable for the task at
+    hand.
     """
 
-    __slots__ = ("_keys", "mapping")
+    __slots__ = ("keys_", "mapping")
 
     def __init__(self, keys: Collection[K], mapping: Mapping[K, V]):
-        self._keys = keys
+        self.keys_ = keys  # .keys is already a property on Mapping
         self.mapping = mapping
 
     def __getitem__(self, key: K) -> V:
+        if key not in self.keys_:
+            raise KeyError(key)
         return self.mapping[key]
 
     def __iter__(self) -> Iterator[K]:
-        return iter(self._keys)
+        return iter(self.keys_)
 
     def __len__(self) -> int:
-        return len(self._keys)
+        return len(self.keys_)
+
+    def __repr__(self) -> str:
+        return f"{type(self).__name__}(keys={self.keys_!r}, mapping={self.mapping!r})"
 
 
 class OrderedSet(MutableSet[T]):

xarray/tests/test_datatree.py

@@ -216,16 +216,16 @@ def test_is_hollow(self):
 
 
 class TestToDataset:
-    def test_to_dataset(self):
-        base = xr.Dataset(coords={"a": 1})
-        sub = xr.Dataset(coords={"b": 2})
+    def test_to_dataset_inherited(self):
+        base = xr.Dataset(coords={"a": [1], "b": 2})
+        sub = xr.Dataset(coords={"c": [3]})
         tree = DataTree.from_dict({"/": base, "/sub": sub})
         subtree = typing.cast(DataTree, tree["sub"])
 
         assert_identical(tree.to_dataset(inherited=False), base)
         assert_identical(subtree.to_dataset(inherited=False), sub)
 
-        sub_and_base = xr.Dataset(coords={"a": 1, "b": 2})
+        sub_and_base = xr.Dataset(coords={"a": [1], "c": [3]})  # no "b"
         assert_identical(tree.to_dataset(inherited=True), base)
         assert_identical(subtree.to_dataset(inherited=True), sub_and_base)
 
@@ -714,7 +714,8 @@ def test_inherited(self):
         dt["child"] = DataTree()
         child = dt["child"]
 
-        assert set(child.coords) == {"x", "y", "a", "b"}
+        assert set(dt.coords) == {"x", "y", "a", "b"}
+        assert set(child.coords) == {"x", "y"}
 
         actual = child.copy(deep=True)
         actual.coords["x"] = ("x", ["a", "b"])
@@ -729,7 +730,7 @@ def test_inherited(self):
 
         with pytest.raises(KeyError):
             # cannot delete inherited coordinate from child node
-            del child["b"]
+            del child["x"]
 
         # TODO requires a fix for #9472
         # actual = child.copy(deep=True)
@@ -1278,22 +1279,23 @@ def test_inherited_coords_index(self):
         assert "x" in dt["/b"].coords
         xr.testing.assert_identical(dt["/x"], dt["/b/x"])
 
-    def test_inherited_coords_override(self):
+    def test_inherit_only_index_coords(self):
         dt = DataTree.from_dict(
             {
-                "/": xr.Dataset(coords={"x": 1, "y": 2}),
-                "/b": xr.Dataset(coords={"x": 4, "z": 3}),
+                "/": xr.Dataset(coords={"x": [1], "y": 2}),
+                "/b": xr.Dataset(coords={"z": 3}),
             }
         )
         assert dt.coords.keys() == {"x", "y"}
-        root_coords = {"x": 1, "y": 2}
-        sub_coords = {"x": 4, "y": 2, "z": 3}
-        xr.testing.assert_equal(dt["/x"], xr.DataArray(1, coords=root_coords))
-        xr.testing.assert_equal(dt["/y"], xr.DataArray(2, coords=root_coords))
-        assert dt["/b"].coords.keys() == {"x", "y", "z"}
-        xr.testing.assert_equal(dt["/b/x"], xr.DataArray(4, coords=sub_coords))
-        xr.testing.assert_equal(dt["/b/y"], xr.DataArray(2, coords=sub_coords))
-        xr.testing.assert_equal(dt["/b/z"], xr.DataArray(3, coords=sub_coords))
+        xr.testing.assert_equal(
+            dt["/x"], xr.DataArray([1], dims=["x"], coords={"x": [1], "y": 2})
+        )
+        xr.testing.assert_equal(dt["/y"], xr.DataArray(2, coords={"y": 2}))
+        assert dt["/b"].coords.keys() == {"x", "z"}
+        xr.testing.assert_equal(
+            dt["/b/x"], xr.DataArray([1], dims=["x"], coords={"x": [1], "z": 3})
+        )
+        xr.testing.assert_equal(dt["/b/z"], xr.DataArray(3, coords={"z": 3}))
 
     def test_inherited_coords_with_index_are_deduplicated(self):
         dt = DataTree.from_dict(

xarray/tests/test_utils.py

@@ -139,6 +139,16 @@ def test_frozen(self):
             "Frozen({'b': 'B', 'a': 'A'})",
         )
 
+    def test_filtered(self):
+        x = utils.FilteredMapping(keys={"a"}, mapping={"a": 1, "b": 2})
+        assert "a" in x
+        assert "b" not in x
+        assert x["a"] == 1
+        assert list(x) == ["a"]
+        assert len(x) == 1
+        assert repr(x) == "FilteredMapping(keys={'a'}, mapping={'a': 1, 'b': 2})"
+        assert dict(x) == {"a": 1}
+
 
 def test_repr_object():
     obj = utils.ReprObject("foo")