pyramid_controllers 0.3

A pyramid plugin that provides de-centralized hierarchical object dispatch.

# pyramid_controllers

The ``pyramid_controllers`` package is a pyramid plugin that provides
de-centralized hierarchical object dispatch, similar to how the
standard TurboGears request dispatch works.

IMPORTANT: in all of the examples below, simple strings are used as
responses. There is nothing in pyramid_controllers that forbids the
use of, or even makes it difficult to use, templating engines. In
fact, this is encouraged but for simplicity has been omitted here.

## Installation

You can manually install it by running ``pip install
pyramid_controllers``. However, a better approach is to use standard
python distribution utilities, and add pyramid_controllers as a
dependency in your project's `install_requires` parameter in your
``setup.py``. Then run a ``python setup.py develop``.

## Usage

First, enable the package either in your INI file via:

```
pyramid.includes = pyramid_controllers
```

or in code in your package's application initialization via:

``` python
def main(global_config, **settings):
# ...
config.include('pyramid_controllers')
# ...
```

Now that your pyramid application has access to the plugin, anchor the
root controller to a URL entrypoint via the
``config.add_controller()`` method. Note that unlike many of the other
controller approaches, a pyramid_controller route takes control of all
URLs that are prefixed with the specified entrypoint. For example, the
following:

``` python
def main(global_config, **settings):
# ...
config.include('pyramid_controllers')
# ...
config.add_controller('rootController', '/root', '.controllers.RootController')
# ...
```

will allow the class ``.controllers.RootController`` to handle any request
for the URL ``/root`` or URLs that start with ``/root/...``.

## Concept

The basic gist of pyramid_controllers is that for any incoming URL, it
will be split into components based on forwarded slashes ("/") and
sequentially lookup the controller in the series while applying name
lookups, defaulting, access control, and generic request manipulation.

For example, assuming that ``RootController`` is anchored at "/", then
the following code will handle a request for ``/how/are/you`` by responding
with the "A-OK!" response.

``` python
from pyramid_controllers import Controller, expose

# note: for simplicity, these classes are defined in order of semantic use.
# for this to actually work, the controllers would need to be defined
# before they are invoked, of course.

class RootController(Controller):
how = HowController()

class HowController(Controller):
are = AreController()

class AreController(Controller):
@expose
def you(self, request):
return 'A-OK!'
```

Here, the initial request is received by ``RootController``. A lookup
of the "how" attribute finds that it is associated with another
controller, so the request is dispatched to that object. The same
thing happens when the ``HowController`` receives the request, which
in turn dispatches it to the ``AreController``. When the framework
does a lookup of the "you" attribute, it finds that it is a method. To
control which methods are invocable via a URL, you must define the
method to be exposed to the framework via the ``@expose`` decorator.

At this point the framework hands the request to the object's method for
handling, providing the active ``request`` object as the first parameter,
in standard pyramid fashion.

TODO: add documentation about the various supported response and
exception types.

## Controllers

There exist two classes that can be subclassed to produce controller
classes:

* **pyramid_controllers.Controller**: this class is the base class
of all controllers, and does not provide much functionality other
than allowing the framework to know that a class is intended to
handle requests in a pyramid_controllers approach.

* **pyramid_controllers.RestController**: this class routes the
various RESTful verbs to controller methods by the same name
(note that the method names are lower-cased).

Here is an example of the latter, which will accept any of the
standard HTTP verbs (GET, PUT, POST, DELETE) to the URL "/hello" and
will emit a response that simply reflects the method used (with a
little poetic licence thrown in):

``` python
from pyramid_controllers import Controller, RestController

class RootController(Controller):
hello = ReflectController()

class ReflectController(RestController):
@expose
def get(self, request):
return 'I am *not* a dog, go GET it yourself!'
@expose
def put(self, request):
return 'Apparently you golf. PUTting is just part of the game.'
@expose
def post(self, request):
return 'People use email today, silly. Stop using the POST!'
@expose
def delete(self, request):
return 'Hey! This is not the CIA, you cannot just DELETE me!'
```

## Decorators

There are several decorators provided by the pyramid_controllers
package that influence how a request is handled, as follows:

* **@expose**: the most common decorator, it simply declares that the
decorated method is intended to handle incoming requests, and is
therefore "exposed" to the public. Note that although it is exposed,
access control restrictions may restrict who can actually access it.

* **@index**: declares that the decorated method is the method that
will handle the request if no further components in the URL path
exist. Think of this as the ``index.html`` in an htdocs directory.

* **@default**: if the standard component lookup strategy fails to
match either a sub-controller or method to handle a request, then
the framework searches for a method that has been decorated as a
``@default`` or ``@lookup`` method (``@lookup`` decorators take
precedence). The default method is expected to behave identically to
an "exposed" method.

* **@lookup**: similar to the ``@default`` decorator, the ``@lookup``
decorator is invoked when the framework could not find another
method or sub-controller to handle the request. The @lookup method,
unlike the @default method, is **not** expected to handle the actual
request, but instead to return a new controller with which the
framework will continue the hierarchical request handling. See below
for details on what parameters are passed and what is expected to be
returned.

* **@fiddle**: a method declared as a "fiddler" will be called before
any other method in the given controller and is expected to do
nothing more than alter the request in some way (such as add
additional attributes) or throw an exception. A fiddler method must
**NOT** be expected to actually respond to a request via standard
methods.

## Complex Example

``` python

from pyramid.httpexceptions import HTTPForbidden, HTTPNotFound

# import the controller base classes
from pyramid_controllers import Controller, RestController

# import the decorators
from pyramid_controllers import expose, index, lookup, default, fiddle

class RootController(Controller):
public = PublicController()
admin = AdminController()
member = MemberDispatchController()

class PublicController(Controller):
login = AuthController()
@expose
def about(self, request):
return 'We are a snazy company!'

class AuthController(RestController):
@expose
def get(self, request):
return '<html><form><input name="u"/><input name="p"/></form></html>'
@expose
def post(self, request):
# todo: perform authentication...

class AdminController(Controller):
@fiddle
def checkAuth(self, request):
if userHasAdminAccess(request): return
raise HTTPForbidden()
@index
def index(self, request):
return 'View the list of <a href="users">active users</a>.'
@expose
def users(self, request):
return '<ul><li>you</li></ul>'

class MemberDispatchController(Controller):
@fiddle
def checkAuth(self, request):
if userHasMemberAccess(request): return
raise HTTPForbidden()
@lookup
def _lookup(self, username, *rem):
user = findUserByUsername(username)
if not user:
raise HTTPNotFound()
return (MemberController(user), rem)

class MemberController(Controller):
def __init__(self, user):
self.user = user
@index
def index(self, request):
return 'Hi, my name is ' + self.user.name
@expose
def age(self, request):
return 'I am %d years old.' % (self.user.age,)
@default
def _default(self, request, attribute, *rem):
return 'My "%s" is "%r".' % (attribute, getattr(self.user, attribute))
```