Convert Tuple attribute of pydantic model to List in json schema

[tamuhey]

Is your feature request related to a problem

I have a model Foo to be used as response class:

from pydantic import BaseModel 

class Foo(BaseModel):
    span: Tuple[int, int]

@app.get("/", response_class=Foo)
async def main():
    return Foo(span=(1, 2))

However, this generates empty typed json schema:

I want Foo to be generated [interger] in json shcema.

The solution you would like

Tuple is converted to List in json schema.

Describe alternatives you've considered

Rewrite Foo.span type annotation to List[int].

[dmontagu]

1. Can you share the full generated schema for the model (not just a Swagger UI screenshot)? I think it should be possible to call Foo.schema() or similar.

2. This probably belongs as a pydantic issue, as fastapi just uses schemas generated by pydantic. You might be better off asking there.

[tamuhey]

1. shcema seems to be correct.

{"openapi":"3.0.2","info":{"title":"Fast API","version":"0.1.0"},"paths":{"/":{"post":{"summary":"Main","operationId":"main__post","requestBody":{"content":{"multipart/form-data":{"schema":{"$ref":"#/components/schemas/Body_main__post"}}},"required":true},"responses":{"200":{"description":"Successful Response","content":{"application/json":{"schema":{"$ref":"#/components/schemas/Foo"}}}},"422":{"description":"Validation Error","content":{"application/json":{"schema":{"$ref":"#/components/schemas/HTTPValidationError"}}}}}}}},"components":{"schemas":{"Body_main__post":{"title":"Body_main__post","required":["file"],"type":"object","properties":{"file":{"title":"File","type":"string","format":"binary"}}},"Foo":{"title":"Foo","required":["span"],"type":"object","properties":{"span":{"title":"Span","type":"array","items":[{"type":"integer"},{"type":"integer"}]}}},"HTTPValidationError":{"title":"HTTPValidationError","type":"object","properties":{"detail":{"title":"Detail","type":"array","items":{"$ref":"#/components/schemas/ValidationError"}}}},"ValidationError":{"title":"ValidationError","required":["loc","msg","type"],"type":"object","properties":{"loc":{"title":"Location","type":"array","items":{"type":"string"}},"msg":{"title":"Message","type":"string"},"type":{"title":"Error Type","type":"string"}}}}}}

Is this a problem to render the schema in /docs page?

[tamuhey]

I pasted the schema to Swagger Editor and confirmed that this schema is invalid.
json schema seems not completely compatible to openAPI.

[tamuhey]

@dmontagu What do you think about?

[dmontagu]

Thanks for following up. Yeah I’m not sure what the best thing to do is here. Given how much there is to support I’m generally okay with it if we just properly support what’s the same in both JSON Schema and OpenAPI. I’d be open to changing the behavior (or trying to get it changed anyway) given enough interest. Or if @tiangolo thinks it’s best.

You can manually override the generated schema using Config.schema_extra so I would just do that for now if you need this (maybe with a utility function if you want to do it in many places).

[tiangolo]

The thing is that OpenAPI explicitly forbids lists with multiple sub-schemas (tuples). So, you can't declare tuples with OpenAPI even though you can with JSON Schema.

If you need to have tuples in your model (i.e. you can't declare it as a list) the best way to go would probably be as @dmontagu says by adding a schema_extra method that updates the schema.

[github-actions[bot]]

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