FastAPI variable query parameters

As mention in docs of FastAPI https://fastapi.tiangolo.com/tutorial/query-params-str-validations/.

 @app.get("/")
 def read_root(param1: Optional[str] = None, param2: Optional[str] = None):
     url = f'http://some.other.api/{param1}/{param2}'
     return {'url': str(url)}

output

If the query parameters are known when starting the API but you still wish to have them dynamically set:

from fastapi import FastAPI, Depends
from pydantic import create_model

app = FastAPI()

# Put your query arguments in this dict
query_params = {"name": (str, "me")}

query_model = create_model("Query", **query_params) # This is subclass of pydantic BaseModel

# Create a route
@app.get("/items")
async def get_items(params: query_model = Depends()):
    params_as_dict = params.dict()
    ...

This has the benefit that you see the parameters in the automatic documentation:

But you are still able to define them dynamically (when starting the API).

Note: if your model has dicts, lists or other BaseModels as field types, the request body pops up. GET should not have body content so you might want to avoid those types.

See more about dynamic model creation from Pydantic documentation.

I use a combination of Depends, BaseModel and the Request object itself.

Here’s an example for a HTTP request like localhost:5000/api?requiredParam1=value1&optionalParam2=value2&dynamicParam1=value3&dynamicParam2=value4

# imports
from typing import Union
from pydantic import BaseModel
from fastapi import Depends, Request

# the base model
class QueryParams(BaseModel):
    required: str
    optional: Union[None, str] = None
    dynamic: dict

# dependency
async def query_params(
    request: Request, requiredParam1: str, optionalParam1: Union[None, str] = None
    ):
    # process the request here
    dynamicParams = {}
    for k in request.query_params.keys():
        if 'dynamicParam' not in k:
            continue
        dynamicParams[k] = request.query_params[k]

    # also maybe do some other things on the arguments
    # ...

    return {
        'required': requiredParam1,
        'optional': optionalParam1,
        'dynamic': dynamicParams
    }

# the endpoint
@app.get("api/")
async def hello(params: QueryParams = Depends(query_params)):

    # Maybe do domething with params here,
    # Use it as you would any BaseModel object
    # ...

    return params

Refer the Starlette documentation on how to use the request object: https://www.starlette.io/requests/

Note that you can put query_params in a different module, and need not add any more code to explicitly pass the Request object. FastAPI already does that when you make a call to the endpoint 🙂

This is a code I derived from @Hajar Razip using a more pydantic like approach:

from pydantic import (
    BaseModel,
)
from typing import (
    Dict,
    List,
    Optional,
)

from fastapi import (
    Depends,
    FastAPI,
    Query,
    Request,
)


class QueryParameters(BaseModel):
    """Model for query parameter."""
    fixId: Optional[str]
    fixStr: Optional[str]
    fixList: Optional[List[str]]
    fixBool: Optional[bool]
    dynFields: Dict

    _aliases: Dict[str,str] = {"id": "fixId"}

    @classmethod
    def parser(
        cls, 
        request: Request,
        fixId: Optional[str] = Query(None, alias="id"),
        fixStr: Optional[str] = Query(None),
        fixList: Optional[List[str]] = Query(None),
        fixBool: bool = Query(True),
    ) -> Dict:
        """Parse query string parameters."""
        dynFields = {}
        reserved_keys = cls.__fields__
        query_keys = request.query_params
        for key in query_keys:
            key = cls._aliases.get(key, key) 
            if key in reserved_keys:
                continue
            dynFields[key] = request.query_params[key]
        
        return {
            "fixId": fixId,
            "fixStr": fixStr,
            "fixList": fixList,
            "fixBool": fixBool,
            "dynFields": dynFields
        }


app = FastAPI()


@app.get("/msg")
def get_msg(
    parameters: QueryParameters = Depends(
            QueryParameters.parser,
    ),
) -> None:
    return parameters

The output documentation is then

Here it is the result of calling GET /msg

> curl -s -X 'GET' 'http://127.0.0.1:8000/msg?id=Victor&fixStr=hi&fixList=eggs&fixList=milk&fixList=oranges&fixBool=true' -H 'accept: application/json' | python3 -m json.tool
{
    "fixId": "Victor",
    "fixStr": "hi",
    "fixList": [
        "eggs",
        "milk",
        "oranges"
    ],
    "fixBool": true,
    "dynFields": {}
}

Here it is the GET /msg call using dynamic fields

>  curl -s -X 'GET' 'http://127.0.0.1:8000/msg?id=Victor&fixStr=hi&fixList=eggs&fixList=milk&fixList=oranges&fixBool=true&key1=value1&key2=value2' -H 'accept: application/json' | python3 -m json.tool
{
    "fixId": "Victor",
    "fixStr": "hi",
    "fixList": [
        "eggs",
        "milk",
        "oranges"
    ],
    "fixBool": true,
    "dynFields": {
        "key1": "value1",
        "key2": "value2"
    }
}