Off-the-shelf functionality¶
Not everyone wants to build everything from scratch. Ideally, one wants to glue together a couple of pre-built components (perhaps mixed with some custom code also) when building a new web application.
User interface concepts in Reahl have been designed specifically to allow bits of user interface to be plugged into many different web applications without forcing the look or layout of the target web application to conform to the reused part.
Reahl web applications can be composed of individually distributed, reusable components. Each such component contains code (including user interface code), information about its roots in the database and the configuration information it needs to run. Infrastructure is provided which allows one to create the database schema for an application that consists of many such components, or migrate data from an older schema to a newer one, etc.
Some pre-built components are also shipped with Reahl.
The code below shows how one would use the shipped functionality that would allow users to register and log into a website:
First, the web application needs to indicate that it uses these components by adding them as dependencies to its .reahlproject file:
<deps purpose="run">
<egg name="reahl-domainui"/>
<egg name="reahl-domain"/>
...
</deps>
In code, the user interface needs to be grafted onto your web application:
Any web application is accessed by means of the URLs it exposes. The URLs of a web application form a hierarchy.
A UserInterface in Reahl is such a hierarchy – but with a twist: A UserInterface can be grafted onto another UserInterface. And that is exactly what happens in the code above: An AccountUI is grafted onto ExampleUI, at the URL “/accounts”. Of course, ExampleUI is also just a UserInterface itself. We just chose to use it as the root of our entire application.
AccountUI has an URL “/login” (amongst others). But, from now on, “/accounts/login” will refer to “/login” of the AccountUI grafted onto “/accounts” in our web application.
class ExampleUI(UserInterface):
def assemble(self):
# some other UserInterfaces added here, and the bookmarks asked from them
self.define_user_interface('/accounts', AccountUI,
{'main_slot': 'maincontent'},
'accounts', bookmarks)