fastapi jinja url_for with query params
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Out of the box Starlette does not support url_for with query params it throws the following error.

Date: April 5, 2024

Out of the box FastAPI </starlette/>.">Starlette does not support url_for with query params. When trying to use url_for with query params it throws the following error.

[code]
  starlette.routing.NoMatchFound: No route exists for name "infinite" and params "page"

In my searching for this I found starlette issue #560 <https://github.com/encode/starlette/issues/560> quite helpful, but not complete, as it did not work for me.

[code]
  import jinja2

  if hasattr(jinja2, "pass_context"):
      pass_context = jinja2.pass_context
  else:
      pass_context = jinja2.contextfunction

  @pass_context
  def url_for_query(context: dict, name: str, **params: dict) -> str:
      request = context["request"]
      url = str(request.url_for(name))
      if params == {}:
          return url
      from urllib.parse import parse_qs, urlencode, urlparse, urlunparse

      # Parse the URL
      parsed_url = urlparse(url)

      # Parse the query parameters
      query_params = parse_qs(parsed_url.query)

      # Update the query parameters with the new ones
      query_params.update(params)

      # Rebuild the query string
      updated_query_string = urlencode(query_params, doseq=True)

      # Rebuild the URL with the updated query string
      updated_url = urlunparse(
          (
              parsed_url.scheme,
              parsed_url.netloc,
              parsed_url.path,
              parsed_url.params,
              updated_query_string,
              parsed_url.fragment,
          )
      )

      if os.environ.get("ENV") in ["dev", "qa", "prod"]:
          updated_url = updated_url.replace("http", "https", 1)

      return updated_url

  def get_templates():
      templates = Jinja2Templates(directory="templates")
      templates.env.globals["url_for"] = url_for_query
      return templates

NOTE https
│ [code]
│    If you want url_for to work in production you need some way to convert http
│ 
│ to https. Here is how I make it work, for local development I export ENV=local then for each environment that I am running on a server I include it in the list and update ENV appropriately.
│ 
│ [code]
│       if os.environ.get("ENV") in ["dev", "qa", "prod"]:
│           updated_url = updated_url.replace("http", "https", 1)

The route might look something like this.

[code]
  @infinite_router.get("/")
  async def home(request: Request, page: int = 1, n: int = 10):
    ...

To access the home route using url_for in a jinja template you can use the following, once you have applied the url_for_query function as your default url_for

[code]
  <a href="{{ url_for('home', page=1) }}">Home</a>