response_model not working for list[] responses

[ermal-abiti]

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Example Code

from fastapi import FastAPI

app = FastAPI()

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


@app.post("/items/", response_model=list[Item], response_model_exclude={"price",})
async def create_item(item: Item):
    return [item]

Description

After I call the /items/ endpoint, i expect the following response as i wanted to exclude price from the model :

[
  {
    "name": "string",
    "description": "string"
  }
]

but I am getting

[
  {
    "name": "string",
    "price": 0,
    "description": "string"
  }
]

Is there any solution for this ?

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.101.0

Pydantic Version

2.1.1

Python Version

3.11

Additional Context

No response

[tojimahammatov]

It worked with fastapi version 0.92.0, pydantic 1.10.5, and python 3.10, though I guess fastapi version matters. response_model_exclude parameter type changed to IncEx (complex Set and Dict types still though) in latest version via fastapi.types where 0.92.0 uses Union[Set, Dict] from fastapi.encoders. Maybe it can help for more debugging. I came up to this point only ).

Most probably, I think we need to provide {"price", } value in a different way.

[JavierSanchezCastro]

Hi!

It's not possible to exclude when the response is a list, also I recommend data filtering.

See the tip

This should work as expected:

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class ItemBase(BaseModel):
    name: str
    description: str

class CreateItem(ItemBase):
    price: float

class ShowItem(ItemBase):
    pass


@app.post("/items/", response_model=list[ShowItem])
async def create_item(item: CreateItem):
    return [item]

[Akashh2151]

It seems like you are trying to exclude the "price" field from the response model when using FastAPI and Pydantic. However, in your current code, the "price" field is still included in the response.

To exclude a field from the response model, you can use the response_model_exclude parameter when defining the route. In your code, you are using it correctly, but there might be a version issue or a mistake in the usage.

In FastAPI 0.101.0, the response_model_exclude parameter should be a set of field names to exclude. However, it seems that it's not working as expected in your case.

Here are a few things you can try to resolve the issue:

Update FastAPI and Pydantic: Ensure that you are using the latest versions of FastAPI and Pydantic. Newer versions may have fixed this issue.

Use a List as a Response Model: Instead of using list[Item] as the response model, try using a List of dictionaries. You can manually create the response format you want. For example:
`from fastapi import FastAPI

app = FastAPI()

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

@app.post("/items/", response_model=list[dict], response_model_exclude={"price"})
async def create_item(item: Item):
return [{"name": item.name, "description": item.description}]
` Check for Any Middlewares or Overrides: Make sure that there are no middlewares or custom response overrides in your FastAPI application that might be modifying the response.
If none of these solutions work, consider upgrading to a newer version of FastAPI, as newer versions often come with bug fixes and improvements. Additionally, check the FastAPI GitHub repository or discussion forums for any known issues related to response_model_exclude for your specific version.