Fix missing imports for nested references when using --collapse-root-models (#2631)

* Add support for collapsing nested references in root models

* Refactor nested reference schemas to use consistent naming conventions

Author: koxudaxi

src/datamodel_code_generator/parser/base.py

@@ -1451,7 +1451,7 @@ def __collapse_root_models(  # noqa: PLR0912
                     else:  # pragma: no cover
                         continue
 
-                    for d in root_type_field.data_type.data_types:
+                    for d in copied_data_type.all_data_types:
                         if d.reference is None:
                             continue
                         from_, import_ = full_path = relative(model.module_name, d.full_name)

tests/data/expected/main/jsonschema/jsonschema_collapse_root_models_nested_reference.py

@@ -0,0 +1,17 @@
+# generated by datamodel-codegen:
+#   filename:  collapse_root_models_nested_reference.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import List
+
+from pydantic import BaseModel
+
+
+class SomeRef(BaseModel):
+    id: str
+
+
+class Model(BaseModel):
+    refs: List[SomeRef]

tests/data/jsonschema/collapse_root_models_nested_reference.json

@@ -0,0 +1,31 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "properties": {
+    "refs": {
+      "$ref": "#/$defs/SomeRefs"
+    }
+  },
+  "required": [
+    "refs"
+  ],
+  "$defs": {
+    "SomeRefs": {
+      "type": "array",
+      "items": {
+        "$ref": "#/$defs/SomeRef"
+      }
+    },
+    "SomeRef": {
+      "type": "object",
+      "properties": {
+        "id": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "id"
+      ]
+    }
+  }
+}

tests/main/jsonschema/test_main_jsonschema.py

@@ -3157,6 +3157,17 @@ def test_main_jsonschema_collapse_root_models_with_optional(output_file: Path) -
     )
 
 
+def test_main_jsonschema_collapse_root_models_nested_reference(output_file: Path) -> None:
+    """Ensure nested references inside root models still get imported when collapsing."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "collapse_root_models_nested_reference.json",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        extra_args=["--collapse-root-models"],
+    )
+
+
 def test_main_jsonschema_file_url_ref(tmp_path: Path) -> None:
     """Test that file:// URL $ref is resolved correctly."""
     pet_schema = {