Slumber is a RESTful data connector that can be used to make proper
RESTful data services from Django systems.

To install Slumber use:

::

    pip install django_slumber

To install the current development version use:

::

    pip install  git+git://github.com/KayEss/django-slumber.git@develop

Using Slumber
=============

Slumber has two parts, the server and client side. A RESTful service can
be used by just adding the server side to an existing Django system. The
client side is useful where you want to connect to the data service from
another Python system, or even if you just want to decouple the
persistence from the user interface layers within Django.

The Slumber server
------------------

In order to start to use Slumber on the server side you simply need to
include it in your ``urls.py`` with something like this:

::

    (r'^slumber/', include('slumber.urls'))

Note that slumber will not accept any anonymous requests. These will
always result in 401 responses. The simplest to configure option is to
make use of local IP based authentication. This is not recommended for
production use, but is useful for development.

The Slumber data client
-----------------------

The data client is to be found at ``slumber.client``. It must be
configured to be told the location of the directory server.

::

    SLUMBER_DIRECTORY='http://localhost:8000/slumber/'

You should also configure a URL prefix for local Slumber accesses. This
is set as below in ``settings.py``. The value shown below is the
default.

::

    SLUMBER_LOCAL='http://localhost:8000/'

In order to fetch objects from the remote end you should import the
client and make use of it:

::

    from slumber import client

    def do_something():
        pizza = client.slumber_test.Pizza.get(pk=1)
        assert pizza

The RemoteForeignKey model field
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``RemoteForeignKey`` model field is used where you want a foreign
key that points to an object on a different data service.

``model_url``
^^^^^^^^^^^^^

Controls whether Slumber will re-write URLs saved in the database to be
relative to the service that it is given. If the URL starts with the
same string as the URL for the specified service then Slumber will
replace that prefix with ``slumber://service/`` before putting the data
into the database and replace that with the service prefix when reading
the data from the database. This means that if you copy a database, for
example, from production to testing all of the URLs will come out
against the correct services on the test server.

The model URL may be specified in the ``slumber:`` form so that the real
URL will be calculated depending on the deployment configuration.

Slumber services
----------------

Services are used when there are multiple RESTful services that all need
to communicate together in order to provide a full system. Services are
known by name and a single Slumber client can talk to multiple services
through the directory server.

All models in a particular Django project can be put into the same
service through the use of the SLUMBER\_SERVICE setting:

::

    SLUMBER_SERVICE = 'takeaway'

This will create a takeaway service that all of the models can be found
within. Now to access a model from the client the service name also
needs to be used:

::

    shopping_cart = slumber.client.takeaway.order.Cart.get(pk=1)

At least one of the projects must now be designated a Slumber directory
and it is configured with the locations of all of the services (i.e. the
``takeaway`` service running within the same project and the ``pizzas``
service running on another port on the same development machine):

::

    SLUMBER_DIRECTORY = {
        'takeaway': 'http://localhost:8000/slumber/takeaway/',
        'pizzas': 'http://localhost:8001/slumber/pizza/',
    }

Note that the directory must list itself. Even more important is that
this is an absolute URL!

On the ``pizza`` service we can now either repeat the exact same
directory configuration, or have it point to the directory on the
``takeaway`` service. I.e. one of the following configurations can be
used:

::

    SLUMBER_DIRECTORY = {
        'takeaway': 'http://localhost:8000/slumber/takeaway/',
        'pizzas': 'http://localhost:8001/slumber/pizza/',
    }

or

::

    SLUMBER_DIRECTORY = 'http://localhost:8000/slumber/'

Django application services
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sometimes it's useful to be able to put a Django application into a
service. There's a few ways of doing this. If it's a single application
that needs to be in a service then the application name can be given as
the location of a service in the ``SLUMBER_DIRECTORY``. For example:

::

    SLUMBER_DIRECTORY = {
        'auth': 'django.contrib.auth',
        'pizzas': 'slumber_examples',
    }

For this to work the application name given in the service configuration
must exactly match the name that is in Django's ``INSTALLED_APPS``
setting. When used in this way the service will point directly to the
Django application mentioned.

''NB'' The current implementation aliases the application to where it is
exposed on the main service. This does expose the requested application,
but fails to remove the application from the main service applications.
I.e. on the above example, both ``auth`` and ``pizzas`` will have all
django.contrib.auth application exposed through the client.

Using a non Slumber Django project for the directory
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Slumber directory doesn't even need to be Django. All that is needed
is that the url that the directory points at returns JSON that describes
where to find the services. The JSON returned for the above example
should look like:

::

    {
        "services": {
            "takeaway": "http://localhost:8000/slumber/takeaway/",
            "pizzas": "http://localhost:8001/slumber/pizza/"
        }
    }

Slumber operations
------------------

Slumber contains a number of default REST end points on the server side
(called operations) which also have a client implementation (called a
proxy). Slumber will expose the applications and the models that you
have in your Django project and currently provides operations at both
the model and instance level.

When dealing with operations that create and modify data it's important
to remember that each operation will run in its own transaction on the
server and cannot be rolled back once done.

create (model)
~~~~~~~~~~~~~~

Creates a new instance of the model type on the slumber server. In order
to use this the user must have the standard ``app.add_model``
permission.

delete (instance)
~~~~~~~~~~~~~~~~~

Uses a POST request to delete the instance. The user requires the
``app.delete_model`` permission.

data (instance)
~~~~~~~~~~~~~~~

Returns the instance attributes and provides links to related data. Only
authenticated users may get instance data.

Customising Slumber data
^^^^^^^^^^^^^^^^^^^^^^^^

When Slumber loads the applications you have defined in your
``settings.py`` it will also try to load a module called
``slumber_conf`` from the same place as your models. This can be used to
customise how models appear on the Slumber server.

::

    from models import Shop
    from slumber import configure

    configure(Shop,
        properties_ro = ['web_site'])

This will make a new read-only property ``web_site`` available in the
data about instances populated from the ``web_site`` property on that
model.

update (instance)
~~~~~~~~~~~~~~~~~

Allows the instance attributes to be changed. The user must have the
``app.change_model`` permission.

Customising Slumber operations
------------------------------

New operations can be added to a model through the configure call. This
should be placed in your ``slumber_server`` file (in
``slumber_server.py`` in your application folder).

::

    from slumber import configure

    configure(Pizza,
        operations_extra = [(OrderPizza, 'order')])

You need to a pass a list of binary tuples which contain the operation
implementation and the name of the operation.

Customising the Slumber client
------------------------------

Operations that you wish to expose on the client side can be added to a
proxy that implements the binding in any way you choose. Proxies come in
two types: model proxies and instance proxies.

When the client creates a model instance to connect to a remote model it
will look for a user defined proxy class and use that as a mix-in super
class for the model type it builds. This allows you to place methods on
the proxy and have them used by your client code.

::

    class ShopProxy(object):
        def has_shop_proxy(self):
            return True

This proxy can be set up by configuring it in your ``slumber_client.py``
file:

::

    configure('/slumber_examples/Shop/',
        model_proxy = ShopProxy)

For the model URL we need to specify enough of the model URL that it
will be unique. Normally just the application and model name are needed,
but sometimes you will want to include service names if you want to have
the same model use different proxies depending on the service it's
connected to.

Note that although this is a model proxy the method on the proxy is
still an instance method and not a class method or static.

Instance proxies are done in exactly the same way, but the configuration
is done via ``instance_proxy`` instead.

::

    class PizzaProxy(object):
        def has_pizza_proxy(self):
            return True

    configure('/slumber_examples/Pizza/',
        instance_proxy = PizzaProxy)

If your proxy needs to find an operation URL then they will appear in
``self._operations``, which is a dict keyed on the operation name given
on the server.

::

    from slumber.connector.ua import get

    def Example(object):
        def proxy_operation(self):
            json = get(self._operations['operation-name'])

This would expect to find an operation name ``operation-name`` on the
server and will issue a GET against it.

Slumber will automatically load the proxies for you when the client is
first used. The packages that contain ``slumber_client`` modules will
need to be listed in the ``SLUMBER_CLIENT_APPS`` setting. I.e.:

::

    SLUMBER_CLIENT_APPS = ['slumber_examples']

This will cause the client to do an import of
``slumber_examples.slumber_client``.

Slumber remote authentication and authorization
-----------------------------------------------

Slumber is also able to help you manage centralised authentication and
authorization across RESTful services. This allows you to make use of
``django.contrib.auth`` on one service to handle permissions on another.

In order to make use of remote authentication you will need to add an
authentication backend. The default Django settings don't include
``AUTHENTICATION_BACKENDS`` so you will need to add this. Typically you
will want to turn off Django's normal authentication back end.

::

    AUTHENTICATION_BACKENDS = [
        'slumber.connector.authentication.Backend',
    ]

Any server can be used as the central store, but to get Slumber to make
use of it Slumber must be properly configured. Continuing our pizza
example from earlier and assuming that we have a Slumber server exposed
at ``http://auth.example.com/slumber/`` we would configure our pizza
service as follows.

::

    SLUMBER_SERVICE = 'pizzas'
    SLUMBER_DIRECTORY = {
        'auth': 'http://auth.example.com/slumber/',
        'pizzas': 'http://localhost:8000/'
    }

Note that the service based configuration must be used and there must be
an ``auth`` service. The ``auth`` service is allowed to be an alias onto
another location. For example, if we had an ``accounting`` service that
was to handle authentication and authorization then we could configure
it using:

::

    SLUMBER_SERVICE = 'accounting'

To use this as the ``auth`` service from elsewhere we would now need to
give the accounting URL as the ``auth`` location to other services.
I.e.:

::

    SLUMBER_DIRECTORY = {
        'auth': 'http://accounting.example.com/slumber/accounting/',
        'accounting': 'http://accounting.example.com/slumber/accounting/',
        'pizzas': 'http://localhost:8000/'
    }

If Slumber needs to pass authenticated requests to another service then
the ``slumber.connector.middleware.ForwardAuthentication`` middleware
needs to be installed.

Caching of requests
-------------------

Slumber includes some simple HTTP request caching within the client
connector. By default this caching is turned off for all models. It can
be enabled on a per model basis by adding proxies for the models and in
the instances and including a ``_CACHE_TTL`` attribute. This will cache
the GET responses for the number of seconds specified in the
time-to-live.

If you include your own GET requests to the user agent in a proxy then
you should remember to pass the cache TTL value:

::

    ua.get(url, self._CACHE_TTL)

See the file ``slumber/connector/proxies.py`` for examples on the User
object.

Doing development
=================

*This project uses git flow. Don't forget to do ``git flow init -d``*
(i.e. use defaults for all options).

First you will want to create virtual environments to run the tests in.
There is a helper script in ``test-projects`` for this.

::

    test-projects/make-virtual-environments

In order to use this you will need virtualenv and virtualenv-wrapper.

Once the virtual environments are created the tests can be run using the
``runtests`` script.

::

    ./runtests

Note that you do not need to be in a virtual environment when you run
this script. It will switch between the required virtual environments
automatically when the tests are run.
