GET Request with Pydantic List field

[Avish021]

Hi,

I'm new to FastAPI (migrating from Flask) and I'm trying to create a Pydantic Model to my GET route

from fastapi import APIRouter,Depends
from pydantic import BaseModel
from typing import Optional,List

router = APIRouter()
class SortModel(BaseModel):
    field:    Optional[str]
    directions: List[str] 

@router.get("/pydanticmodel")
def get_sort(criteria: SortModel = Depends(SortModel)):
    pass #my code for handling this route.....

When I'm running curl -X GET http://localhost:XXXX/pydanticmodel?directions=up&directions=asc&field=id I'm getting 422 Unprocessable Entity: {"detail":[{"loc":["body"],"msg":"field required","type":"value_error.missing"}]}

But if I'm changing directions:List[str] -> directions: str I'm getting 200 OK with directions="asc".

What is the reason that str works for query param and List[str] does not? what am I doing wrong?

Thanks.

[SirTelemak]

directions: List[str] means pydantic should expect array of values on validation, but you can't send [ and ] inside query. Unfortunately FastAPI can't work with such case to pass multiple arguments via Depends using pydantic model. Best scenario for you is:

class SortModel(BaseModel):

    field:    Optional[str]
    directions: List[str]


def sort_model(field: Optional[str] = Query(None), directions: List[str] = Query([])):
    return SortModel(field=field, directions=directions)


@router.get("/pydanticmodel")
def get_sort(sort: SortModel = Depends(sort_model)):

[ycd]

@SirTelemak Yes you can't send an array inside query but you can send a body with -d flag, the code works fine when you send a Body with using -d flag

In: curl -X GET "http://127.0.0.1:8000/pydanticmodel?field=123"  -d "[\"string\"]"
Out: {"field":"123","directions":["string"]}

[SirTelemak]

@ycd ye, but it's quite unintuitive and works bad with OpenAPI so I think better way to use like I suggested, so you can use
curl -X GET "http://127.0.0.1:8000/pydanticmodel?field=123&directions=value1&directions=value2"

[Avish021]

Hi everybody,

Thank you for your replies.
Another issue arises since in my real model have like 15 other fields. I would like to avoid passing them as explicit parameters in the sort_model function (since its just repeating the declarations in the model)

Do you know any other way to avoid it?
In addition, thoughts about this work-around?

def add_sort(request:Request):
    d = {}
    for (key, value) in request.query_params._list:
        if key not in d:
            d[key] = value
        else:
            if d[key] is not List:
                current_value = d[key]
                d[key] = [current_value]

            d[key].append( value )

    return SortModel( **d )

[krishnardt]

Instead of using basemodel, you can use and validate directly through Python class if in case you are getting the data from a form.

class SortModel:
    def __init__(self,
     field= Optional[str]= Form(),
     directions = Optional[str]=Form()):

    self.field = field
    self.directions = directions

@router.get("/pydanticmodel")
def get_sort(criteria: SortModel = Depends()):
    pass #my code for handling this route.....

this will work out for form validation..

[ycd]

@ycd ye, but it's quite unintuitive and works bad with OpenAPI so I think better way to use like I suggested, so you can use
curl -X GET "http://127.0.0.1:8000/pydanticmodel?field=123&directions=value1&directions=value2"

Actually, that's what Swagger suggests for the query.

[masreplay]

@tiangolo any help

[jonocodes]

Just chiming in here since I am having the same issue. When defining a list in a basemodel, the swagger spec moves that query parameter into the body. I dont know if the issue lies in the pydantic model or in the swagger spec generator.

[YuriiMotov]

Since FastAPI 0.115.0 you can officially use Pydantic models to declare Query parameters:

from fastapi import FastAPI, Query
from pydantic import BaseModel
from typing import Optional, List

app = FastAPI()


class SortModel(BaseModel):
    field: Optional[str]
    directions: List[str]


@app.get("/pydanticmodel")
def get_sort(criteria: SortModel = Query()):
    pass  # my code for handling this route.....

Docs: https://fastapi.tiangolo.com/tutorial/query-param-models/