Lazy route

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Unreleased
 
 ## New Features
+* `routing.lazy_route` - allows you to lazily load Forms whilst using routing
+  https://github.com/anvilistas/anvil-extras/pull/442
 * Autocompletion: adds filter_mode property - either contains or startswith
   https://github.com/anvilistas/anvil-extras/discussions/444
 

client_code/routing/__init__.py

@@ -12,7 +12,7 @@
 from . import _navigation
 from . import _router as _r
 from ._alert import alert
-from ._decorators import error_form, redirect, route, template
+from ._decorators import error_form, lazy_route, redirect, route, template
 from ._logging import logger
 from ._router import NavigationExit, launch
 from ._utils import (

client_code/routing/_decorators.py

@@ -93,3 +93,24 @@ def error_form(cls):
     cls._route_props = {"title": None, "layout_props": {}}
     _router._error_form = cls
     return cls
+
+
+def lazy_route(
+    url_pattern="", url_keys=[], title=None, full_width_row=False, template=None
+):
+    route_wrapper = route(url_pattern, url_keys, title, full_width_row, template)
+
+    def wrapper(fn):
+        class Lazy:
+            _form = None
+
+            def __new__(cls, **properties):
+                form_class = cls._form
+                if form_class is None:
+                    form_class = cls._form = fn()
+                return form_class.__new__(form_class, **properties)
+
+        route_wrapper(Lazy)
+        return fn
+
+    return wrapper

docs/guides/modules/routing.rst

@@ -389,6 +389,22 @@ Decorators
         If the ``before_unload`` method is added it will be called whenever the form currently in the ``content_panel`` is about to be removed.
         If any truthy value is returned then unloading will be prevented. See `Form Unloading <#form-unloading>`__.
 
+.. function:: routing.lazy_route(url_pattern, url_keys=[], title=None, full_width_row=False, template=None)
+
+    .. code:: python
+
+        from anvil_extras import routing
+
+        @routing.lazy_route('article', url_keys=['id', routing.ANY], title="Article-{id} | RoutingExample")
+        def article_route():
+            from ..ArticleForm import ArticleForm
+            return ArticleForm
+
+    This decorator allows you to lazily load Forms. When using ``@routing.route`` all Forms that are routes must be imported before the app starts.
+    This is fine for most small applications, but as your application grows you may find that executing all the code for all the Forms is slow.
+    The ``lazy_route`` decorator should decorate a function that imports the Form and returns it.
+
+
 .. function:: routing.redirect(path, priority=0, condition=None)
 
     The redirect decorator can decorate a function that will intercept the current navigtation, depending on its ``path``, ``priority`` and ``condition`` arguments.