From 125a52fefd5ef6cea68f8e19a7e42b3e592a76fb Mon Sep 17 00:00:00 2001 From: masaaya <156692516+mkanetsuna@users.noreply.github.com> Date: Sun, 28 Dec 2025 02:42:43 +0900 Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Fix=20Form()=20with=20Pydantic?= =?UTF-8?q?=20Json[T]=20type=20(#10997)?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- fastapi/dependencies/utils.py | 8 +- tests/test_form_json_type.py | 325 ++++++++++++++++++++++++++++++++++ 2 files changed, 332 insertions(+), 1 deletion(-) create mode 100644 tests/test_form_json_type.py diff --git a/fastapi/dependencies/utils.py b/fastapi/dependencies/utils.py index 45e1ff3ed1..dc168455ae 100644 --- a/fastapi/dependencies/utils.py +++ b/fastapi/dependencies/utils.py @@ -716,11 +716,17 @@ def _validate_value_with_model_field( return v_, [] +def _is_pydantic_json_field(field: ModelField) -> bool: + return any(item.__class__.__name__ == 'Json' for item in field.field_info.metadata) + + def _get_multidict_value( field: ModelField, values: Mapping[str, Any], alias: Union[str, None] = None ) -> Any: alias = alias or get_validation_alias(field) - if is_sequence_field(field) and isinstance(values, (ImmutableMultiDict, Headers)): + if _is_pydantic_json_field(field): + value = values.get(alias, None) + elif is_sequence_field(field) and isinstance(values, (ImmutableMultiDict, Headers)): value = values.getlist(alias) else: value = values.get(alias, None) diff --git a/tests/test_form_json_type.py b/tests/test_form_json_type.py new file mode 100644 index 0000000000..2dd94073c0 --- /dev/null +++ b/tests/test_form_json_type.py @@ -0,0 +1,325 @@ +""" +Test cases for Form() with Pydantic Json[T] type. +Regression tests for issue #10997. +https://github.com/fastapi/fastapi/issues/10997 + +Before the fix: Json[list[str]] with Form() would wrap values in extra list +After the fix: _is_pydantic_json_field() ensures correct single value extraction +""" + +import json +from pathlib import Path +from typing import Annotated + +from dirty_equals import IsDict +from fastapi import FastAPI, File, Form, UploadFile +from fastapi.testclient import TestClient +from pydantic import BaseModel, Json + +app = FastAPI() + + +# ============================================================================ +# Endpoints +# ============================================================================ + + +@app.post("/form-json-list") +def form_json_list(items: Annotated[Json[list[str]], Form()]) -> list[str]: + """Primary bug case - Json[list[str]] with Form().""" + return items + + +@app.post("/form-json-dict") +def form_json_dict(data: Annotated[Json[dict[str, str]], Form()]) -> dict[str, str]: + """Json[dict] parsing.""" + return data + + +@app.post("/form-json-optional") +def form_json_optional( + items: Annotated[Json[list[str]] | None, Form()] = None +) -> dict: + """Optional Json field.""" + return {"items": items, "received": items is not None} + + +@app.post("/form-json-with-regular-fields") +def form_json_with_regular_fields( + username: Annotated[str, Form()], + tags: Annotated[Json[list[str]], Form()], + age: Annotated[int, Form()], +) -> dict: + """Json field mixed with regular Form fields.""" + return {"username": username, "tags": tags, "age": age} + + +class FormWithJsonModel(BaseModel): + """Pydantic model with Json field for Form().""" + + username: str + tags: Json[list[str]] + + +@app.post("/form-json-model") +def form_json_model(form: Annotated[FormWithJsonModel, Form()]) -> FormWithJsonModel: + """Json field in Pydantic model with Form().""" + return form + + +@app.post("/form-json-with-file") +def form_json_with_file( + tags: Annotated[Json[list[str]], Form()], + file: UploadFile = File(...), +) -> dict: + """Json field with File() parameter.""" + return {"tags": tags, "filename": file.filename} + + +@app.post("/form-regular-list") +def form_regular_list(items: Annotated[list[str], Form()]) -> list[str]: + """Regular list Form field (without Json wrapper) - must still work.""" + return items + + +# ============================================================================ +# Test Client +# ============================================================================ + +client = TestClient(app) + + +# ============================================================================ +# Core Functionality Tests +# ============================================================================ + + +def test_form_json_list_str(): + """Test Form() + Json[list[str]] - primary bug case for issue #10997. + + Before the fix, this would incorrectly wrap the JSON string in a list: + Input: '["abc", "def"]' + Bug: [['["abc", "def"]']] (wrapped in extra list) + Fix: ["abc", "def"] (correctly parsed) + """ + response = client.post( + "/form-json-list", + data={"items": json.dumps(["abc", "def"])}, + ) + assert response.status_code == 200, response.text + result = response.json() + + # Verify correct parsing + assert result == ["abc", "def"] + + # Explicitly verify NOT the buggy wrapped version + assert result != [['["abc", "def"]']] + + +def test_form_json_dict(): + """Test Form() + Json[dict] - dictionary parsing.""" + test_data = {"name": "John", "city": "NYC"} + response = client.post( + "/form-json-dict", + data={"data": json.dumps(test_data)}, + ) + assert response.status_code == 200, response.text + assert response.json() == test_data + + +# ============================================================================ +# Edge Cases Tests +# ============================================================================ + + +def test_form_json_optional_with_none(): + """Test optional Json field with no value sent.""" + response = client.post("/form-json-optional", data={}) + assert response.status_code == 200, response.text + result = response.json() + assert result["items"] is None + assert result["received"] is False + + +def test_form_json_optional_with_value(): + """Test optional Json field with value provided.""" + response = client.post( + "/form-json-optional", + data={"items": json.dumps(["test"])}, + ) + assert response.status_code == 200, response.text + result = response.json() + assert result["items"] == ["test"] + assert result["received"] is True + + +def test_form_json_empty_values(): + """Test Json fields with empty array and object.""" + # Empty list + response = client.post( + "/form-json-list", + data={"items": json.dumps([])}, + ) + assert response.status_code == 200, response.text + assert response.json() == [] + + # Empty dict + response = client.post( + "/form-json-dict", + data={"data": json.dumps({})}, + ) + assert response.status_code == 200, response.text + assert response.json() == {} + + +def test_form_json_with_regular_fields(): + """Test Json field mixed with regular Form fields.""" + response = client.post( + "/form-json-with-regular-fields", + data={ + "username": "alice", + "tags": json.dumps(["python", "fastapi"]), + "age": "30", + }, + ) + assert response.status_code == 200, response.text + assert response.json() == { + "username": "alice", + "tags": ["python", "fastapi"], + "age": 30, + } + + +# ============================================================================ +# Error Handling Tests +# ============================================================================ + + +def test_form_json_missing_required(): + """Test missing required Json field returns validation error.""" + response = client.post("/form-json-list", data={}) + assert response.status_code == 422, response.text + error_detail = response.json() + # Note: input can be None or {} depending on form data processing + assert error_detail == IsDict( + { + "detail": [ + { + "type": "missing", + "loc": ["body", "items"], + "msg": "Field required", + "input": None, + } + ] + } + ) | IsDict( + { + "detail": [ + { + "type": "missing", + "loc": ["body", "items"], + "msg": "Field required", + "input": {}, + } + ] + } + ) | IsDict( + # Pydantic v1 compatibility + { + "detail": [ + { + "loc": ["body", "items"], + "msg": "field required", + "type": "value_error.missing", + } + ] + } + ) + + +# ============================================================================ +# Integration Tests +# ============================================================================ + + +def test_form_json_with_pydantic_model(): + """Test Json field in Pydantic model with Form().""" + response = client.post( + "/form-json-model", + data={ + "username": "alice", + "tags": json.dumps(["python", "fastapi"]), + }, + ) + assert response.status_code == 200, response.text + assert response.json() == { + "username": "alice", + "tags": ["python", "fastapi"], + } + + +def test_form_json_with_file_upload(tmp_path: Path): + """Test Json field with File() parameter in multipart form.""" + temp_file = tmp_path / "test.txt" + temp_file.write_text("test content") + + response = client.post( + "/form-json-with-file", + data={"tags": json.dumps(["important", "urgent"])}, + files={"file": ("test.txt", temp_file.read_bytes())}, + ) + assert response.status_code == 200, response.text + result = response.json() + assert result["tags"] == ["important", "urgent"] + assert result["filename"] == "test.txt" + + +def test_form_json_doesnt_break_regular_sequences(): + """Test that regular list Form fields still work correctly. + + This is critical: the fix for Json[T] must not break existing + Form list behavior. Regular list fields should still use getlist() + for multiple form values. + """ + response = client.post( + "/form-regular-list", + data={"items": ["x", "y", "z"]}, + ) + assert response.status_code == 200, response.text + assert response.json() == ["x", "y", "z"] + + +# ============================================================================ +# OpenAPI Schema Test +# ============================================================================ + + +def test_openapi_schema_json_field(): + """Test that OpenAPI schema correctly represents Json fields as string type. + + In OpenAPI, Json[T] form fields should be represented as string type + (not the inner type like array or object), because the form data contains + a JSON string that will be parsed by Pydantic, not the parsed structure. + """ + response = client.get("/openapi.json") + assert response.status_code == 200, response.text + + schema = response.json() + paths = schema["paths"] + + # Check /form-json-list endpoint + endpoint_schema = paths["/form-json-list"]["post"] + assert "application/x-www-form-urlencoded" in endpoint_schema["requestBody"]["content"] + + # Get body schema + body_schema_ref = endpoint_schema["requestBody"]["content"][ + "application/x-www-form-urlencoded" + ]["schema"]["$ref"] + schema_name = body_schema_ref.split("/")[-1] + body_schema = schema["components"]["schemas"][schema_name] + + # Verify Json[list[str]] is represented as string in OpenAPI + items_field = body_schema["properties"]["items"] + assert items_field["type"] == "string", ( + f"Json[list[str]] should be 'string' type in OpenAPI, got {items_field}" + )