Can FastAPI/OpenAPI support multiple response models?

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Yes, FastAPI/OpenAPI supports multiple response models. You can define multiple response models in the OpenAPI specification using the responses section with different response codes. For example:

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

class ErrorResponse(BaseModel):
    message: str

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    if item_id == 0:
        return {"error": "item_id must be greater than zero"}
    elif item_id == 1:
        return ErrorResponse(message="Item not found")
    else:
        return Item(name="Item " + str(item_id), price=1.23)

In the example above, we define two response models: Item and ErrorResponse. We use Item as the response model for successful requests and ErrorResponse as the response model for error requests. The responses section in the OpenAPI specification will show the different models for each possible response code.