fix(config): validate subcategory parent sampler type

packages/data-designer-config/src/data_designer/config/data_designer_config.py

@@ -54,10 +54,15 @@ def _validate_subcategory_parents(self) -> Self:
             if col.column_type != "sampler" or col.sampler_type != SamplerType.SUBCATEGORY:
                 continue
             parent = by_name.get(col.params.category)
-            if parent is not None and parent.column_type != "sampler":
+            if parent is not None and (parent.column_type != "sampler" or parent.sampler_type != SamplerType.CATEGORY):
+                if parent.column_type == "sampler":
+                    parent_sampler_type = getattr(parent.sampler_type, "value", parent.sampler_type)
+                    parent_type = f"sampler column with sampler_type='{parent_sampler_type}'"
+                else:
+                    parent_type = f"'{parent.column_type}' column"
                 raise ValueError(
-                    f"Subcategory column '{col.name}' has parent '{parent.name}', which is a "
-                    f"'{parent.column_type}' column. Subcategory parents must be sampler columns "
+                    f"Subcategory column '{col.name}' has parent '{parent.name}', which is a {parent_type}. "
+                    f"Subcategory parents must be sampler columns "
                     f"with sampler_type='category'."
                 )
         return self

packages/data-designer-config/tests/config/test_data_designer_config.py

@@ -183,6 +183,31 @@ def test_subcategory_parent_as_category_sampler_is_valid() -> None:
     assert len(config.columns) == 2
 
 
+def test_subcategory_parent_must_be_a_category_sampler() -> None:
+    with pytest.raises(ValueError, match=r"sampler_type='uniform'.*sampler_type='category'"):
+        DataDesignerConfig.model_validate(
+            {
+                "columns": [
+                    {
+                        "name": "package_type",
+                        "column_type": "sampler",
+                        "sampler_type": "uniform",
+                        "params": {"low": 0, "high": 1},
+                    },
+                    {
+                        "name": "ski_category",
+                        "column_type": "sampler",
+                        "sampler_type": "subcategory",
+                        "params": {
+                            "category": "package_type",
+                            "values": {"basic": ["a"], "premium": ["b"]},
+                        },
+                    },
+                ]
+            }
+        )
+
+
 def test_subcategory_parent_missing_defers_to_schema_validator() -> None:
     config = DataDesignerConfig.model_validate(
         {