Unexpected ValidationError with accessing /openapi.json when some model uses typing.Tuple

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn’t find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google “How to X in FastAPI” and didn’t find any information.
• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from pydantic import BaseModel
from fastapi import FastAPI

from typing import Tuple

class FooModel(BaseModel):
  prop: Tuple[int, str]


app = FastAPI()

@app.get('/', response_model=FooModel)
def get_foo():
 return {"prop": (0, 'ok')}

print(app.openapi())

Description

Summary

The above code must be failed with a ValidationError like this:

Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    a()
  File "<pyshell#1>", line 17, in a
    print(app.openapi())
  File "/usr/local/lib/python39/lib/site-packages/fastapi/applications.py", line 136, in openapi
    self.openapi_schema = get_openapi(
  File "/usr/local/lib/python39/lib/site-packages/fastapi/openapi/utils.py", line 410, in get_openapi
    return jsonable_encoder(OpenAPI(**output), by_alias=True, exclude_none=True)  # type: ignore
  File "pydantic/main.py", line 406, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 2 validation errors for OpenAPI
components -> schemas -> FooModel -> properties -> prop -> items
  value is not a valid dict (type=type_error.dict)
components -> schemas -> FooModel -> $ref
  field required (type=value_error.missing)

in fastapi.openapi.models in line 103~142

class Schema(BaseModel):
    ref: Optional[str] = Field(None, alias="$ref")
    title: Optional[str] = None
    multipleOf: Optional[float] = None
    maximum: Optional[float] = None
    exclusiveMaximum: Optional[float] = None
    minimum: Optional[float] = None
    exclusiveMinimum: Optional[float] = None
    maxLength: Optional[int] = Field(None, gte=0)
    minLength: Optional[int] = Field(None, gte=0)
    pattern: Optional[str] = None
    maxItems: Optional[int] = Field(None, gte=0)
    minItems: Optional[int] = Field(None, gte=0)
    uniqueItems: Optional[bool] = None
    maxProperties: Optional[int] = Field(None, gte=0)
    minProperties: Optional[int] = Field(None, gte=0)
    required: Optional[List[str]] = None
    enum: Optional[List[Any]] = None
    type: Optional[str] = None
    allOf: Optional[List["Schema"]] = None
    oneOf: Optional[List["Schema"]] = None
    anyOf: Optional[List["Schema"]] = None
    not_: Optional["Schema"] = Field(None, alias="not")
    items: Optional["Schema"] = None
    properties: Optional[Dict[str, "Schema"]] = None
    additionalProperties: Optional[Union["Schema", Reference, bool]] = None
    description: Optional[str] = None
    format: Optional[str] = None
    default: Optional[Any] = None
    nullable: Optional[bool] = None
    discriminator: Optional[Discriminator] = None
    readOnly: Optional[bool] = None
    writeOnly: Optional[bool] = None
    xml: Optional[XML] = None
    externalDocs: Optional[ExternalDocumentation] = None
    example: Optional[Any] = None
    deprecated: Optional[bool] = None

    class Config:
        extra: str = "allow"

It seems Schema.items should accept an array of schemas according to the JSON schema spec, but only the type Schema is allowed in the current code.

Operating System

Linux, Windows

Operating System Details

No response

FastAPI Version

0.70.0

Python Version

Python 3.9.5

Additional Context

No response

[HansBrende]

+1! Also, duplicate of #3665, #3686, #3782, and #3898 (the list is growing!)

[oligond]

nitp - Your sample code has a small issue that might confuse people, so you probably want to fix that for posteriority:

The return value of your sample route is an array, but, according to the model declaration, it’s supposed to be a dict containing a prop key which has a tuple of (int, str) as value:

@app.get('/', response_model=FooModel)
def get_foo():
 return {"prop": (0, 'ok')}