Route Class¶

The Route class is used to define routes for your app. When a user navigates to a path, the router will look for a matching route. The router will call anvil.open_form on the matching route's form.

# routes.py
from routing.router import Route

class IndexRoute(Route):
    path = "/"
    form = "Pages.Index"

class AboutRoute(Route):
    path = "/about"
    form = "Pages.About"

class ContactRoute(Route):
    path = "/contact"
    form = "Pages.Contact"

The above code can use the Route.create() method for convenience:

# routes.py
from routing.router import Route

IndexRoute = Route.create(path="/", form="Pages.Index")
AboutRoute = Route.create(path="/about", form="Pages.About")
ContactRoute = Route.create(path="/contact", form="Pages.Contact")

Route Attributes¶

path: The path to navigate to. e.g. /, /articles or /articles/:id.
form: The form to open when the route is matched. e.g. Pages.Index.
error_form (optional): The form to open when an error occurs. e.g. Pages.Error.
not_found_form (optional): The form to open when the route is not found. e.g. Pages.NotFound.
pending_form (optional): The form to open when the data is loading. e.g. Pages.Loading.
pending_delay=1: The delay before showing the pending form when the data is loading.
pending_min=0.5: The minimum time to show the pending form when the data is loading.
cache_data=False: Whether to cache data. By default this is False.
gc_time=30*60: The time in seconds that determines when data is released from the cache for garbage collection. By default this is 30 minutes. When data is released from the cache, any cached forms with the same path and cache_deps will also be released.
server_fn (optional str): The server function to call when the route is matched. e.g. "get_article". This server function will be called with the same keyword arguments as the route's load_data method. Note this is optional and equivalent to defining a load_data method that calls the same server function.
server_silent=False: If True then the server function will be called using anvil.server.call_s. By default this is False.

Route Methods¶

before_load: Called before the route is matched. This method can raise a Redirect exception to redirect to a different route. By default this returns None.
parse_query: Should return a dictionary of query parameters. By default this returns the original query parameters.
parse_params: Should return a dictionary of path parameters. By default this returns the original path parameters.
meta: Should return a dictionary with the title and description of the page. This will be used to update the meta tags and the title of the page. By default this returns the original title and description.
load_data: Called when the route is matched. The return value will be available in the data property of the RoutingContext instance. By default this returns None.
load_form: This method is called with two arguments. The first argument is a form name (e.g. "Pages.Index") or, if you are using cached forms, the cached form instance. The second argument is the RoutingContext instance. By default this calls anvil.open_form on the form.
cache_deps: Caching is determined by the path and the return value of the cache_deps method. The default implementation returns the query dictionary. That is, a route with the same path and query will be considered to be the same route. And routes with different query will be considered to be different routes.

Not Found Form¶

There are two ways a route can be not found. The first is when the user navigates to a path that does not match any routes. The second is when a user raises a NotFound exception in a route's before_load or load_data method.

Not Found Route¶

By definition, if there is no matching route, the router has no route to navigate to. If you want to handle this case, you can define a not found route.

from routing.router import Route

class NotFoundRoute(Route):
    form = "Pages.NotFound"
    default_not_found = True

The NotFoundRoute will be used when the user navigates to a path that does not match any routes. The path attribute should not be set, since this will be determined based on the path the user navigates to.

If no default_not_found attribute is set, then the router will raise a NotFound exception, which will be caught by Anvil's exception handler.

Raising a NotFound Exception¶

If you raise a NotFound exception in a route's before_load or load_data method, the router will call the route's load_form method with the route's not found form.

from routing.router import Route

class ArticleRoute(Route):
    path = "/articles/:id"
    form = "Pages.Article"
    not_found_form = "Pages.ArticleNotFound"

    def load_data(self, **loader_args):
        id = loader_args["params"]["id"]
        article = app_tables.articles.get(id=id)
        if article is None:
            raise NotFound(f"No article with id {id}")
        return article

If a route raises a NotFound exception and there is no not_found_form attribute, the router will raise the exception, which will be caught by Anvil's exception handler.

Error Form¶

When a route throws an exception, the router will call anvil.open_form on the matching route's error form.

If no error form is defined, the error will be caught by Anvil's exception handler.

from routing.router import Route

# Either define the error form globally
Route.error_form = "Pages.Error"

# or define the error form per route
class IndexRoute(Route):
    path = "/"
    form = "Pages.Index"
    error_form = "Pages.Error"

# Pages.Error
import anvil

class Error(ErrorTemplate):
    def __init__(self, routing_context: RoutingContext, **properties):
        self.init_components(**properties)
        self.routing_context = routing_context
        self.label.text = (
            f"Error when navigating to {routing_context.path!r}, got {routing_context.error!r}"
        )

    def form_show(self, **event_args):
        if anvil.app.environment.name.startswith("Debug"):
            raise self.routing_context.error

Ordering Routes¶

The router will try to match routes in the order they are defined.

from routing.router import Route

class AuthorsRoute(Route):
    path = "/authors"
    form = "Pages.Authors"

class NewAuthorRoute(Route):
    path = "/authors/new"
    form = "Pages.NewAuthor"

class AuthorRoute(Route):
    path = "/authors/:id"
    form = "Pages.Author"

In the above example, it's important that the NewAuthorRoute comes before the AuthorRoute in the list of routes. This is because /authors/new is a valid path for the AuthorRoute, so the router would successfully match the route and open the form.

Server Routes¶

When a user navigates to a URL directly, the router will match routes on the server.

When you import your routes in server code, the router will automatically create a server route for each route.

# ServerRoutes.py
from . import routes

Under the hood this will look something like:

# ServerRoutes.py
from . import routes

# pseudo code - for illustration only
for route in Routes.__subclasses__():
    if route.path is None:
        continue

    @anvil.server.route(route.path)
    def server_route(**params):
        ...
        # return a response object that will open the form on the client