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[BUG] NewType breaks OpenAPI generation

See original GitHub issue

Describe the bug FastAPI fails to generate openapi.json when the schema contains types declared with typing.NewType

To Reproduce Steps to reproduce the behavior:

Create a file failme.py with contents:

from typing import NewType
from fastapi import FastAPI, Query, Body

app = FastAPI()

Identifier = NewType("Identifier", int)

@app.post("/inpath/{num}")
async def inpath(num: Identifier) -> str:
    return f"2*num={2*num}"

@app.post("/inquery/")
async def inquery(num: Identifier = Query(...)) -> str:
    return f"2*num={2*num}"

@app.post("/inbody/")
async def inbody(num: Identifier = Body(...)) -> str:
    return f"2*num={2*num}"

Run the app:

uvloop failme:app

Navigate to http://127.0.0.1:8000/docs
The documentation is not rendered in the web page. The command line shows the error:

[...]
  File ".../lib/python3.7/site-packages/fastapi/applications.py", line 87, in openapi
    return JSONResponse(self.openapi())
  File ".../lib/python3.7/site-packages/fastapi/applications.py", line 79, in openapi
    openapi_prefix=self.openapi_prefix,
  File ".../lib/python3.7/site-packages/fastapi/openapi/utils.py", line 254, in get_openapi
    result = get_openapi_path(route=route, model_name_map=model_name_map)
  File ".../lib/python3.7/site-packages/fastapi/openapi/utils.py", line 163, in get_openapi_path
    all_route_params=all_route_params
  File ".../lib/python3.7/site-packages/fastapi/openapi/utils.py", line 87, in get_openapi_operation_parameters
    "schema": field_schema(param, model_name_map={})[0],
  File "pydantic/schema.py", line 288, in pydantic.schema.field_schema
  File "pydantic/schema.py", line 518, in pydantic.schema.field_type_schema
  File "pydantic/schema.py", line 745, in pydantic.schema.field_singleton_schema
TypeError: issubclass() arg 1 must be a class

Expected behavior The OpenAPI documentation to be rendered rendered.

Screenshots

Environment:

OS: Linux
FastAPI Version 0.35.0
Python version: 3.7.3

Issue Analytics

State:
Created 4 years ago
Comments:6 (3 by maintainers)

Top GitHub Comments

4reactions

zamiramircommented, Sep 3, 2019

FYI: Resolved in #463

4reactions

dmontagucommented, Sep 3, 2019

@Victor-Savu @xyb #423 was replaced with a different PR upgrading to newer pydantic. It is now merged; as of 0.38 NewType works for schema generation.

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