From f1e6f978ce10a6f9b4c668350a79462e9ac330a8 Mon Sep 17 00:00:00 2001
From: vvanglro <947001731@qq.com>
Date: Sun, 21 Sep 2025 02:51:40 +0800
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=EF=B8=8F=20Fix=20`default=5Ffactory`?=
 =?UTF-8?q?=20for=20response=20model=20field=20with=20Pydantic=20V1=20(#97?=
 =?UTF-8?q?04)?=
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Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>
---
 fastapi/utils.py                             |  1 +
 tests/test_response_model_default_factory.py | 47 ++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 tests/test_response_model_default_factory.py

diff --git a/fastapi/utils.py b/fastapi/utils.py
index 4c7350fea..98725ff19 100644
--- a/fastapi/utils.py
+++ b/fastapi/utils.py
@@ -137,6 +137,7 @@ def create_cloned_field(
     new_field.alias = field.alias  # type: ignore[misc]
     new_field.class_validators = field.class_validators  # type: ignore[attr-defined]
     new_field.default = field.default  # type: ignore[misc]
+    new_field.default_factory = field.default_factory  # type: ignore[attr-defined]
     new_field.required = field.required  # type: ignore[misc]
     new_field.model_config = field.model_config  # type: ignore[attr-defined]
     new_field.field_info = field.field_info
diff --git a/tests/test_response_model_default_factory.py b/tests/test_response_model_default_factory.py
new file mode 100644
index 000000000..13c1f442b
--- /dev/null
+++ b/tests/test_response_model_default_factory.py
@@ -0,0 +1,47 @@
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from pydantic import BaseModel, Field
+
+app = FastAPI()
+
+
+class ResponseModel(BaseModel):
+    code: int = 200
+    message: str = Field(default_factory=lambda: "Successful operation.")
+
+
+@app.get(
+    "/response_model_has_default_factory_return_dict",
+    response_model=ResponseModel,
+)
+async def response_model_has_default_factory_return_dict():
+    return {"code": 200}
+
+
+@app.get(
+    "/response_model_has_default_factory_return_model",
+    response_model=ResponseModel,
+)
+async def response_model_has_default_factory_return_model():
+    return ResponseModel()
+
+
+client = TestClient(app)
+
+
+def test_response_model_has_default_factory_return_dict():
+    response = client.get("/response_model_has_default_factory_return_dict")
+
+    assert response.status_code == 200, response.text
+
+    assert response.json()["code"] == 200
+    assert response.json()["message"] == "Successful operation."
+
+
+def test_response_model_has_default_factory_return_model():
+    response = client.get("/response_model_has_default_factory_return_model")
+
+    assert response.status_code == 200, response.text
+
+    assert response.json()["code"] == 200
+    assert response.json()["message"] == "Successful operation."