Check that the mapping is valid after setting it.

python/mlcroissant/mlcroissant/_src/datasets.py

@@ -46,6 +46,16 @@ def get_operations(ctx: Context, metadata: Metadata) -> OperationGraph:
     return operations
 
 
+def _check_mapping(metadata: Metadata, mapping: Mapping[str, epath.Path]):
+    """Checks that the mapping is valid, i.e. keys are actual UUIDs and paths exist."""
+    uuids = set([node.uuid for node in metadata.nodes()])
+    for uuid, path in mapping.items():
+        if uuid not in uuids:
+            raise ValueError(f"{uuid=} in the mapping doesn't exist in the JSON-LD")
+        if not path.exists():
+            raise ValueError(f"{path=} doesn't exist on disk")
+
+
 def _expand_mapping(
     mapping: Mapping[str, epath.PathLike] | None,
 ) -> Mapping[str, epath.Path]:
@@ -83,6 +93,7 @@ def __post_init__(self):
             self.metadata = Metadata.from_file(ctx=ctx, file=self.jsonld)
         else:
             return
+        _check_mapping(self.metadata, ctx.mapping)
         # Draw the structure graph for debugging purposes.
         if self.debug:
             graphs_utils.pretty_print_graph(ctx.graph)

python/mlcroissant/mlcroissant/_src/datasets_test.py

@@ -88,6 +88,7 @@ def load_records_and_test_equality(
     record_set_name: str,
     num_records: int,
     filters: dict[str, Any] | None = None,
+    mapping: dict[str, epath.PathLike] | None = None,
 ):
     filters_command = ""
     if filters:
@@ -109,7 +110,7 @@ def load_records_and_test_equality(
     with output_file.open("rb") as f:
         lines = f.readlines()
         expected_records = [json.loads(line) for line in lines]
-    dataset = datasets.Dataset(config)
+    dataset = datasets.Dataset(config, mapping=mapping)
     records = dataset.records(record_set_name, filters=filters)
     records = iter(records)
     length = 0
@@ -330,3 +331,31 @@ def test_validate_filters(filters, raises):
             datasets._validate_filters(filters)
     else:
         datasets._validate_filters(filters)
+
+
+@parametrize_version()
+def test_check_mapping_when_the_key_does_not_exist(version):
+    dataset_name = "simple-parquet/metadata.json"
+    record_set_name = "persons"
+    with pytest.raises(ValueError, match="doesn't exist in the JSON-LD"):
+        load_records_and_test_equality(
+            version,
+            dataset_name,
+            record_set_name,
+            -1,
+            mapping={"this_UUID_does_not_exist": "/this/path/does/not/exist"},
+        )
+
+
+@parametrize_version()
+def test_check_mapping_when_the_path_does_not_exist(version):
+    dataset_name = "simple-parquet/metadata.json"
+    record_set_name = "persons"
+    with pytest.raises(ValueError, match="doesn't exist on disk"):
+        load_records_and_test_equality(
+            version,
+            dataset_name,
+            record_set_name,
+            -1,
+            mapping={"dataframe": "/this/path/does/not/exist"},
+        )