[Bug] Dataclass optional not working in validate query

[weiztech]

Describe the bug
I'm following this tutorial https://sanic.dev/en/plugins/sanic-ext/validation.html#implementation .
with define dataclass attribute with optional paramater,
it will return 400 , if the query params q have value ex q=123123
without value it will work without problem

I also found the same issue when using pydantic

Screenshots

To Reproduce

from dataclasses import dataclass, asdict
from typing import Optional

from sanic import Sanic
from sanic.response import json
from sanic_ext import validate


app = Sanic("Sanic-APP")


@dataclass
class SearchParams:
    q: Optional[str] = None


@app.route("/")
@validate(query=SearchParams)
async def handler(request, query: SearchParams):
    return json(asdict(query))

Expected behavior
when the dataclass attribute is Optional, it should not error when we send the query params with value ex ?q=123456

Environment (please complete the following information):

• OS: Mac Catalina v10.15.7
• Browser Chrome
• Version 103.0.5060.53

[miss85246]

@weiztech Hi, there.
In GET method, One parameter can have multiple values, like this:

http://localhost:3000/?q=1&q=2&q=3

Most of the time, you don't need to use this feature. one parameter can have only one value.

So, sanic do some process in RequestParameters object.

def get(self, name: str, default: Optional[Any] = None) -> Optional[Any]:
    """Return the first value, either the default or actual"""
    return super().get(name, [default])[0]


def getlist(self, name: str, default: Optional[Any] = None) -> Optional[Any]:
    """
    Return the entire list
    """
    return super().get(name, default)

print(request.args.get("q"))
# 1

print(request.args.getlist("q"))
# [1, 2, 3]

Of course, all of these are based on the RequestParameters operations.

If you print request.args, you will see:

print(request.args)
# {'q': ['1', '2']}
# {'q': ['1']}

It's a dict whose value is a list.

And In sanic-ext validator, the do_validation function use request.args as the source of data. You got the validation Error is merited.

Now, you can use dataclass like this to solve this problem temporarily.

@dataclass
class SearchParams:
    q: Optional[List[str]] = None

I hope this will help you.

[weiztech]

@miss85246 ,

Thanks for let me know the temporary fix. it's really help me 😊😊
Hope the issue will be fixed in future

[ahopkins]

So, what makes this one a little different is the Optional. If you left that part off it should work. A fix is coming shortly though for the optional.