Router refactoring in 0.21


First generation (v1) of router has mapped (method, path) pair to web-handler. Mapping is named route. Routes used to have unique names if any.

The main mistake with the design is coupling the route to (method, path) pair while really URL construction operates with resources (location is a synonym). HTTP method is not part of URI but applied on sending HTTP request only.

Having different route names for the same path is confusing. Moreover named routes constructed for the same path should have unique non overlapping names which is cumbersome is certain situations.

From other side sometimes it’s desirable to bind several HTTP methods to the same web handler. For v1 router it can be solved by passing ‘*’ as HTTP method. Class based views require ‘*’ method also usually.


The change introduces resource as first class citizen:

resource = router.add_resource('/path/{to}', name='name')

Resource has a path (dynamic or constant) and optional name.

The name is unique in router context.

Resource has routes.

Route corresponds to HTTP method and web-handler for the method:

route = resource.add_route('GET', handler)

User still may use wildcard for accepting all HTTP methods (maybe we will add something like resource.add_wildcard(handler) later).

Since names belongs to resources now app.router['name'] returns a resource instance instead of aiohttp.web.AbstractRoute.

resource has .url() method, so app.router['name'].url(parts={'a': 'b'}, query={'arg': 'param'}) still works as usual.

The change allows to rewrite static file handling and implement nested applications as well.

Decoupling of HTTP location and HTTP method makes life easier.

Backward compatibility

The refactoring is 99% compatible with previous implementation.

99% means all example and the most of current code works without modifications but we have subtle API backward incompatibles.

app.router['name'] returns a aiohttp.web.AbstractResource instance instead of aiohttp.web.AbstractRoute but resource has the same resource.url(...) most useful method, so end user should feel no difference.

route.match(...) is not supported anymore, use aiohttp.web.AbstractResource.resolve() instead.

app.router.add_route(method, path, handler, name='name') now is just shortcut for:

resource = app.router.add_resource(path, name=name)
route = resource.add_route(method, handler)
return route

app.router.register_route(...) is still supported, it creates aiohttp.web.ResourceAdapter for every call (but it’s deprecated now).