When creating an mlc.Metadata object, share the graph with all node…

…s. (#713)

python/mlcroissant/mlcroissant/_src/structure_graph/base_node.py

@@ -214,7 +214,15 @@ def parent(self) -> "Node | None":
     @property
     def predecessors(self) -> set["Node"]:
         """Predecessors in the structure graph."""
-        return set(self.ctx.graph.predecessors(self))  # pytype: disable=bad-return-type
+        try:
+            predecessors = self.ctx.graph.predecessors(self)
+            return set(predecessors)  # pytype: disable=bad-return-type
+        except KeyError as e:
+            raise KeyError(
+                f"Could not find node '{self.id}' in the graph. Make sure to build a"
+                " full mlcroissant metadata object (mlc.Metadata) wrapping all the"
+                " FileSets/FileObjects/RecordSets/Fields."
+            )
 
     @property
     def recursive_predecessors(self) -> set["Node"]:

python/mlcroissant/mlcroissant/_src/structure_graph/nodes/metadata.py

@@ -334,6 +334,10 @@ def __post_init__(self):
             self.ctx, self.ctx.conforms_to
         )
 
+        # Share the structure graph in the context
+        for node in self.nodes():
+            node.ctx.graph = self.ctx.graph
+
     def to_json(self) -> Json:
         """Converts the `Metadata` to JSON."""
         context = self.ctx.rdf.context

python/mlcroissant/mlcroissant/_src/structure_graph/nodes/metadata_test.py

@@ -14,6 +14,7 @@
 from mlcroissant._src.core.issues import ValidationError
 from mlcroissant._src.structure_graph.base_node import Node
 from mlcroissant._src.structure_graph.nodes.creative_work import CreativeWork
+from mlcroissant._src.structure_graph.nodes.field import Field
 from mlcroissant._src.structure_graph.nodes.metadata import Metadata
 from mlcroissant._src.structure_graph.nodes.record_set import RecordSet
 from mlcroissant._src.tests.nodes import create_test_node
@@ -175,3 +176,18 @@ def test_validate_license():
     ]
     with pytest.raises(ValidationError, match="License should be a list of str"):
         Metadata(name="foo", license=42)  # pytype: disable=wrong-arg-types
+
+
+def test_predecessors_are_propagated():
+    field = Field(
+        id="records/name",
+        name="name",
+        data_types=constants.DataType.TEXT,
+    )
+    record_set = RecordSet(
+        id="records",
+        fields=[field],
+        data=[{"name": "train"}, {"name": "test"}],
+    )
+    Metadata(name="dummy", record_sets=[record_set])
+    assert field.predecessors == {record_set}