From 6c6bdb62337ab2e05438d99fce66113e375ddb04 Mon Sep 17 00:00:00 2001
From: dmontagu <35119617+dmontagu@users.noreply.github.com>
Date: Fri, 30 Aug 2019 16:56:14 -0700
Subject: [PATCH] :lock: Ensure `skip_defaults` doesn't cause extra fields to
 be serialized (#485)

---
 fastapi/routing.py          | 4 ++--
 tests/test_skip_defaults.py | 8 ++++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fastapi/routing.py b/fastapi/routing.py
index 930cbe001..08f43bf52 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -45,6 +45,8 @@ def serialize_response(
 ) -> Any:
     if field:
         errors = []
+        if skip_defaults and isinstance(response, BaseModel):
+            response = response.dict(skip_defaults=skip_defaults)
         value, errors_ = field.validate(response, {}, loc=("response",))
         if isinstance(errors_, ErrorWrapper):
             errors.append(errors_)
@@ -52,8 +54,6 @@ def serialize_response(
             errors.extend(errors_)
         if errors:
             raise ValidationError(errors)
-        if skip_defaults and isinstance(response, BaseModel):
-            value = response.dict(skip_defaults=skip_defaults)
         return jsonable_encoder(
             value,
             include=include,
diff --git a/tests/test_skip_defaults.py b/tests/test_skip_defaults.py
index 8579b50ea..9997ba7b2 100644
--- a/tests/test_skip_defaults.py
+++ b/tests/test_skip_defaults.py
@@ -16,9 +16,13 @@ class Model(BaseModel):
     sub: SubModel
 
 
+class ModelSubclass(Model):
+    y: int
+
+
 @app.get("/", response_model=Model, response_model_skip_defaults=True)
-def get() -> Model:
-    return Model(sub={})
+def get() -> ModelSubclass:
+    return ModelSubclass(sub={}, y=1)
 
 
 client = TestClient(app)