Fastapi: [BUG] - FastAPI Routes don't work with Starlette's request.url_for when query params are passed

[cjw296]

Describe the bug
It looks like Starlette's routes are not populating self.param_convertors so, when using request.url_for and passing query parameters, the route does not match (I think this is the code) and url_for fails with a NoMatchFound

To Reproduce
I think this view will do it, sorry if I've elided anything important:

@router.get("/", name='events_list')
def list_object(
    offset: int = Query(0),
    request: Request = Required
):
            next = request.url_for('events_list', offset=42)
            ...

Expected behavior
I'd expect url_for to return something like 'http://testserver/events/?offset=42'

Actual behavior

../diary/api/events.py:57: in list_object
    next = request.url_for('events_list', offset=42)
/Users/chris/Library/Caches/pypoetry/virtualenvs/diary-py3.7/lib/python3.7/site-packages/starlette/requests.py:117: in url_for
    url_path = router.url_path_for(name, **path_params)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <fastapi.routing.APIRouter object at 0x105e855f8>, name = 'events_list'
path_params = {'offset': 42}
route = <fastapi.routing.APIRoute object at 0x106c5ecf8>

    def url_path_for(self, name: str, **path_params: str) -> URLPath:
        for route in self.routes:
            try:
                return route.url_path_for(name, **path_params)
            except NoMatchFound:
                pass
>       raise NoMatchFound()
E       starlette.routing.NoMatchFound

Environment:

• FastAPI Version [e.g. 0.3.0], get it with: 0.30.0

[euri10]

kind of remember having been bitten by this
worth trying to not use name but _name @router.get("/", _name='events_list')

edit: scrap that it was when I had name in the path
On Fri, Jun 21, 2019 at 9:27 AM Chris Withers [e-mail]
wrote:

Describe the bug
It looks like Starlette's routes are not populating self.param_convertors
so, when using request.url_for and passing query parameters, the route
does not match (I think this is the code
https://github.com/encode/starlette/blob/8c8cc2ec0a5cb834a9a15b871ae8b480503abb67/starlette/routing.py#L190)
and url_for fails with a NoMatchFound

To Reproduce
I think this view will do it, sorry if I've elided anything important:

@router.get("/", name='events_list')
def list_object(
offset: int = Query(0),
request: Request = Required
):
next = request.url_for('events_list', offset=42)
...

Expected behavior
I'd expect url_for to return something like '
http://testserver/events/?offset=42'

Actual behavior

../diary/api/events.py:57: in list_object
next = request.url_for('events_list', offset=42)
/Users/chris/Library/Caches/pypoetry/virtualenvs/diary-py3.7/lib/python3.7/site-packages/starlette/requests.py:117: in url_for
url_path = router.url_path_for(name, **path_params)

---

self = , name = 'events_list'
path_params = {'offset': 42}
route =

def url_path_for(self, name: str, **path_params: str) -> URLPath:
    for route in self.routes:
        try:
            return route.url_path_for(name, **path_params)
        except NoMatchFound:
            pass

  raise NoMatchFound()

E starlette.routing.NoMatchFound

Environment:

• FastAPI Version [e.g. 0.3.0], get it with: 0.30.0

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[tiangolo]

I see you discovered the problem and requested the feature here: https://github.com/encode/starlette/issues/560

So I'll close this issue now, as that would actually be a Starlette feature request.

---

For completeness, for anyone coming afterwards, request.url_for() receives path parameters, not query parameters.

[jacksmith15]

For anyone interested in doing this themselves, the following code may be useful.

https://gist.github.com/jacksmith15/b220686eae16d52a10ef59b5de09c213

This goes a bit further than starlette's feature request, as it leverages FastAPI's parameter validation to prevent bad URLs being generated.