Fix allOf array property merging to preserve child $ref (#2962)

* Fix allOf array property merging to preserve child $ref

* Fix filename mismatch in test fixture

* Rename test fixtures to descriptive names

Author: koxudaxi

src/datamodel_code_generator/parser/jsonschema.py

@@ -1870,7 +1870,10 @@ def _merge_property_schemas(self, parent_dict: dict[str, Any], child_dict: dict[
 
         for key, value in child_dict.items():
             if key in result and isinstance(result[key], dict) and isinstance(value, dict):
-                result[key] = self._merge_property_schemas(result[key], value)
+                if "$ref" in value:
+                    result[key] = value
+                else:
+                    result[key] = self._merge_property_schemas(result[key], value)
             else:
                 result[key] = value
         return result

tests/data/expected/main/openapi/allof_array_ref_override.py

@@ -0,0 +1,48 @@
+# generated by datamodel-codegen:
+#   filename:  allof_array_ref_override.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Any
+from uuid import UUID
+
+from pydantic import AwareDatetime, BaseModel, Field, conint
+
+
+class DataType(BaseModel):
+    property_1: UUID | None = Field(
+        None, description='Unique identifier for the installation.'
+    )
+    property_2: str | None = Field(None, description='Description of the installation.')
+    property_3: AwareDatetime | None = Field(
+        None, description='Timestamp when the installation was created.'
+    )
+
+
+class Metadata(BaseModel):
+    limit: conint(ge=1, le=100) = Field(
+        ..., description='Number of data types returned in this response', examples=[20]
+    )
+    page: conint(ge=1) = Field(
+        ..., description='The page number to retrieve', examples=[2]
+    )
+
+
+class CollectionWrapper(BaseModel):
+    """
+    Generic response wrapper containing a collection of items and pagination metadata.
+    """
+
+    data: list[dict[str, Any]] = Field(
+        ..., description='Array of items in the collection.'
+    )
+    pagination: Metadata = Field(
+        ..., description='Pagination metadata for the collection.'
+    )
+
+
+class PaginatedDataTypeList(CollectionWrapper):
+    data: list[DataType] | None = Field(
+        None, description='Array of items in the collection.'
+    )

tests/data/openapi/allof_array_ref_override.yaml

@@ -0,0 +1,65 @@
+openapi: "3.0.0"
+info:
+    title: Issue 2953 Test
+    version: "1.0.0"
+components:
+    schemas:
+        Collection-Wrapper:
+            description: Generic response wrapper containing a collection of items and pagination metadata.
+            type: object
+            required:
+                - data
+                - pagination
+            properties:
+                data:
+                    description: Array of items in the collection.
+                    type: array
+                    items:
+                        type: object
+                pagination:
+                    description: Pagination metadata for the collection.
+                    $ref: "#/components/schemas/Metadata"
+        DataType:
+            type: object
+            required:
+                - id
+            properties:
+                property_1:
+                    type: string
+                    format: uuid
+                    readOnly: true
+                    description: Unique identifier for the installation.
+                property_2:
+                    type: string
+                    description: Description of the installation.
+                property_3:
+                    type: string
+                    format: date-time
+                    readOnly: true
+                    description: Timestamp when the installation was created.
+
+        PaginatedDataTypeList:
+            allOf:
+                - properties:
+                      data:
+                          type: array
+                          items:
+                              $ref: "#/components/schemas/DataType"
+                - $ref: "#/components/schemas/Collection-Wrapper"
+        Metadata:
+            type: object
+            required:
+                - limit
+                - page
+            properties:
+                limit:
+                    type: integer
+                    minimum: 1
+                    maximum: 100
+                    description: Number of data types returned in this response
+                    example: 20
+                page:
+                    type: integer
+                    minimum: 1
+                    description: The page number to retrieve
+                    example: 2

tests/main/openapi/test_main_openapi.py

@@ -4942,25 +4942,24 @@ def test_main_openapi_deprecated_field(output_file: Path) -> None:
 
 
 @SKIP_PYDANTIC_V1
-def test_main_openapi_reuse_scope_tree_single_file_error(capsys: pytest.CaptureFixture[str], output_file: Path) -> None:
-    """Test --reuse-scope=tree with single file output raises proper error (#2953).
+def test_main_openapi_allof_array_ref_no_duplicate_model(output_file: Path) -> None:
+    """Test allOf with array property referencing another schema (#2959).
 
-    When using reuse-scope=tree with single file output and duplicate models,
-    it should raise a proper error about needing a directory output instead of
-    crashing with IndexError.
+    When allOf merges an array property from parent (with generic items) and child
+    (with $ref items), the child's $ref should completely override the parent,
+    preventing duplicate model generation like 'Datum' class.
     """
     run_main_and_assert(
-        input_path=OPEN_API_DATA_PATH / "issue_2953.yaml",
+        input_path=OPEN_API_DATA_PATH / "allof_array_ref_override.yaml",
         output_path=output_file,
         input_file_type="openapi",
-        expected_exit=Exit.ERROR,
-        capsys=capsys,
-        expected_stderr_contains="Modular references require an output directory, not a file",
+        assert_func=assert_file_content,
+        expected_file="allof_array_ref_override.py",
         extra_args=[
             "--output-model-type",
             "pydantic_v2.BaseModel",
-            "--reuse-model",
-            "--reuse-scope",
-            "tree",
+            "--use-standard-collections",
+            "--use-union-operator",
+            "--use-schema-description",
         ],
     )