diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py index fc5dfed85a..060e26c2e1 100644 --- a/fastapi/dependencies/utils.py +++ b/fastapi/dependencies/utils.py @@ -741,6 +741,11 @@ def _get_multidict_value( if field.required: return else: + # For FormData, return None to let Pydantic handle defaults + # This preserves model_fields_set metadata correctly + if isinstance(values, FormData): + return + # For non-FormData (Query, Header, Cookie), keep existing behavior return deepcopy(field.default) return value diff --git a/tests/test_forms_fields_set.py b/tests/test_forms_fields_set.py new file mode 100644 index 0000000000..8140dc24db --- /dev/null +++ b/tests/test_forms_fields_set.py @@ -0,0 +1,139 @@ +""" +Tests for Form fields preserving model_fields_set metadata. +Related to issue #13399: https://github.com/fastapi/fastapi/issues/13399 + +This test validates that Form models correctly track which fields were +explicitly provided vs. which fields use defaults. +""" + +from typing import Annotated + +from fastapi import FastAPI, Form +from fastapi._compat import PYDANTIC_V2 +from fastapi.testclient import TestClient +from pydantic import BaseModel + + +class FormModelFieldsSet(BaseModel): + """Model for testing fields_set metadata preservation.""" + + field_1: bool = True + field_2: str = "default" + field_3: int = 42 + + +app = FastAPI() + + +@app.post("/form-fields-set") +async def form_fields_set_endpoint(model: Annotated[FormModelFieldsSet, Form()]): + # Use correct attribute name for each Pydantic version + if PYDANTIC_V2: + fields_set = list(model.model_fields_set) + else: + fields_set = list(model.__fields_set__) + return { + "fields_set": fields_set, + "data": model.dict() if not PYDANTIC_V2 else model.model_dump(), + } + + +@app.post("/body-fields-set") +async def body_fields_set_endpoint(model: FormModelFieldsSet): + # Use correct attribute name for each Pydantic version + if PYDANTIC_V2: + fields_set = list(model.model_fields_set) + else: + fields_set = list(model.__fields_set__) + return {"fields_set": fields_set} + + +client = TestClient(app) + + +class TestFormFieldsSetMetadata: + """Test that Form models correctly preserve fields_set metadata.""" + + def test_form_empty_data_has_empty_fields_set(self): + """Form with no data should have empty fields_set (matching JSON behavior).""" + resp = client.post("/form-fields-set", data={}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == [] + + def test_body_empty_data_has_empty_fields_set(self): + """JSON body with no data should have empty fields_set.""" + resp = client.post("/body-fields-set", json={}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == [] + + def test_form_partial_data_tracks_provided_fields(self): + """Form with partial data should only show provided fields in fields_set.""" + resp = client.post("/form-fields-set", data={"field_1": "False"}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == ["field_1"] + + def test_body_partial_data_tracks_provided_fields(self): + """JSON body with partial data should only show provided fields.""" + resp = client.post("/body-fields-set", json={"field_1": False}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == ["field_1"] + + def test_form_all_fields_provided(self): + """Form with all fields should show all fields in fields_set.""" + resp = client.post( + "/form-fields-set", + data={"field_1": "False", "field_2": "test", "field_3": "100"}, + ) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert set(fields_set) == {"field_1", "field_2", "field_3"} + + def test_body_all_fields_provided(self): + """JSON body with all fields should show all fields in fields_set.""" + resp = client.post( + "/body-fields-set", + json={"field_1": False, "field_2": "test", "field_3": 100}, + ) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert set(fields_set) == {"field_1", "field_2", "field_3"} + + def test_form_field_set_to_default_value_is_tracked(self): + """Form field explicitly set to default value should appear in fields_set.""" + # Same as default=True, but explicitly provided + resp = client.post("/form-fields-set", data={"field_1": "True"}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == ["field_1"] + + def test_body_field_set_to_default_value_is_tracked(self): + """JSON body field explicitly set to default value should appear in fields_set.""" + resp = client.post("/body-fields-set", json={"field_1": True}) + assert resp.status_code == 200, resp.text + fields_set = resp.json()["fields_set"] + assert fields_set == ["field_1"] + + def test_form_body_consistency(self): + """ + Verify that body and form behave consistently. + Form fields_set should match JSON body fields_set for equivalent data. + """ + # Empty data - both should have empty fields_set + body_resp = client.post("/body-fields-set", json={}) + form_resp = client.post("/form-fields-set", data={}) + assert body_resp.json()["fields_set"] == [] + assert form_resp.json()["fields_set"] == [] + + # Partial data - both should track same fields + body_resp = client.post( + "/body-fields-set", json={"field_1": False, "field_3": 99} + ) + form_resp = client.post( + "/form-fields-set", data={"field_1": "False", "field_3": "99"} + ) + assert set(body_resp.json()["fields_set"]) == {"field_1", "field_3"} + assert set(form_resp.json()["fields_set"]) == {"field_1", "field_3"} diff --git a/tests/test_forms_single_model.py b/tests/test_forms_single_model.py index 7d03d29572..a1c958a715 100644 --- a/tests/test_forms_single_model.py +++ b/tests/test_forms_single_model.py @@ -99,13 +99,13 @@ def test_no_data(): "type": "missing", "loc": ["body", "username"], "msg": "Field required", - "input": {"tags": ["foo", "bar"], "with": "nothing"}, + "input": {}, # Fixed: defaults no longer included (issue #13399) }, { "type": "missing", "loc": ["body", "lastname"], "msg": "Field required", - "input": {"tags": ["foo", "bar"], "with": "nothing"}, + "input": {}, # Fixed: defaults no longer included (issue #13399) }, ] }