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The core of a service layer that integrates with the
Pyramid Web Framework <https://docs.pylonsproject.org/projects/pyramid>
__.
pyramid_services
defines a pattern and helper methods for accessing a
pluggable service layer from within your Pyramid apps.
Install from PyPI <https://pypi.python.org/pypi/pyramid_services>
__ using
pip
or easy_install
inside a virtual environment.
.. code-block:: bash
$ $VENV/bin/pip install pyramid_services
Or install directly from source.
.. code-block:: bash
$ git clone https://github.com/mmerickel/pyramid_services.git $ cd pyramid_services $ $VENV/bin/pip install -e .
Activate pyramid_services
by including it into your pyramid application.
.. code-block:: python
config.include('pyramid_services')
This will add some new directives to your Configurator
.
config.register_service(obj, iface=Interface, context=Interface, name='')
This method will register a service object for the supplied
iface
, context
, and name
. This effectively registers a
singleton for your application as the obj
will always be returned when
looking for a service.
config.register_service_factory(factory, iface=Interface, context=Interface, name='')
This method will register a factory for the supplied iface
,
context
, and name
. The factory should be a callable accepting a
context
and a request
and should return a service object. The
factory will be used at most once per request
/context
/name
combination.
config.set_service_registry(registry)
This method will let you set a custom wired.ServiceRegistry
instance
which is the backing registry for all services.
After registering services with the Configurator
, they are now
accessible from the request
object during a request lifecycle via the
request.find_service(iface=Interface, context=_marker, name='')
method. Unless a custom context
is passed to find_service
, the
lookup will default to using request.context
. The context
will default
to None
if a service is searched for during or before traversal in Pyramid
when there may not be a request.context
.
.. code-block:: python
svc = request.find_service(ILoginService)
Some services (like your database connection) may need a transaction manager
and the best way to do that is by using pyramid_tm
and hooking the
request.tm
transaction manager into your service container. The
request object itself is already added to the container for the
pyramid.interfaces.IRequest
interface and can be used in factories that
require the request.
This can be done before any services are instantiated by subscribing to the
pyramid_services.NewServiceContainer
event:
.. code-block:: python
from pyramid_services import NewServiceContainer
def on_new_container(event): container = event.container request = event.request container.set(request.tm, name='tm')
config.add_subscriber(on_new_container, NewServiceContainer)
Let's create a login service by progressively building up from scratch what we want to use in our app.
Basically all of the steps in configuring an interface are optional, but they are shown here as best practices.
.. code-block:: python
from zope.interface import Interface
class ILoginService(Interface): def create_token_for_login(name): pass
With our interface we can now define a conforming instance.
.. code-block:: python
class DummyLoginService(object): def create_token_for_login(self, name): return 'u:{0}'.format(name)
Let's hook it up to our application.
.. code-block:: python
from pyramid.config import Configurator
from myapp.services import DummyLoginService
def main(global_config, **settings): config = Configurator() config.include('pyramid_services')
config.register_service(DummyLoginService(), ILoginService)
config.add_route('home', '/')
config.scan('.views')
return config.make_wsgi_app()
Finally, let's create our view that utilizes the service.
.. code-block:: python
@view_config(route_name='home', renderer='json') def home_view(request): name = request.params.get('name', 'bob')
login_svc = request.find_service(ILoginService)
token = login_svc.create_token_for_login(name)
return {'access_token': token}
If you start up this application, you will find that you can access the home url and get custom tokens!
This is cool, but what's even better is swapping in a new service without
changing our view at all. Let's define a new PersistentLoginService
that gets tokens from a database. We're going to need to setup some
database handling, but again nothing changes in the view.
.. code-block:: python
from uuid import uuid4
from myapp.model import AccessToken
class PersistentLoginService(object): def init(self, dbsession): self.dbsession = dbsession
def create_token_for_login(self, name):
token = AccessToken(key=uuid4(), user=name)
self.dbsession.add(token)
return token.key
Below is some boilerplate for configuring a model using the excellent
SQLAlchemy ORM <http://docs.sqlalchemy.org>
__.
.. code-block:: python
from sqlalchemy import engine_from_config from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker from sqlalchemy.schema import Column from sqlalchemy.types import Text
Base = declarative_base()
def init_model(settings): engine = engine_from_config(settings) dbmaker = sessionmaker() dbmaker.configure(bind=engine) return dbmaker
class AccessToken(Base): tablename = 'access_token'
key = Column(Text, primary_key=True)
user = Column(Text, nullable=False)
Now we will update the application to use the new PersistentLoginService
.
However, we may have other services and it'd be silly to create a new
database connection for each service in a request. So we'll also add a
service that encapsulates the database connection. Using this technique
we can wire services together in the service layer.
.. code-block:: python
from pyramid.config import Configurator import transaction import zope.sqlalchemy
from myapp.model import init_model from myapp.services import PersistentLoginService
def main(global_config, **settings): config = Configurator() config.include('pyramid_services') config.include('pyramid_tm')
dbmaker = init_model(settings)
def dbsession_factory(context, request):
dbsession = dbmaker()
# register the session with pyramid_tm for managing transactions
zope.sqlalchemy.register(dbsession, transaction_manager=request.tm)
return dbsession
config.register_service_factory(dbsession_factory, name='db')
def login_factory(context, request):
dbsession = request.find_service(name='db')
svc = PersistentLoginService(dbsession)
return svc
config.register_service_factory(login_factory, ILoginService)
config.add_route('home', '/')
config.scan('.views')
return config.make_wsgi_app()
And finally the home view will remain unchanged.
.. code-block:: python
@view_config(route_name='home', renderer='json') def home_view(request): name = request.params.get('name', 'bob')
login_svc = request.find_service(ILoginService)
token = login_svc.create_token_for_login(name)
return {'access_token': token}
Hopefully this pattern is clear. It has several advantages over most basic Pyramid tutorials.
The model is completely abstracted from the views, making both easy to test on their own.
The service layer can be developed independently of the views, allowing for dummy implementations for easy creation of templates and frontend logic. Later, the real service layer can be swapped in as it's developed, building out the backend functionality.
Most services may be implemented in such a way that they do not depend on Pyramid or a particular request object.
Different services may be returned based on a context, such as the result of traversal or some other application-defined discriminator.
If you are writing an application that uses pyramid_services
you may want
to do some integration testing that verifies that your application has
successfully called register_service
or register_service_factory
. Using
Pyramid
's testing
module to create a Configurator
and after calling
config.include('pyramid_services')
you may use find_service_factory
to
get information about a registered service.
Take as an example this test that verifies that dbsession_factory
has been
correctly registered. This assumes you have a myapp.services
package that
contains an includeme()
function.
.. code-block:: python
from myapp.services import dbsession_factory, login_factory, ILoginService
class TestIntegration_services(unittest.TestCase): def setUp(self): self.config = pyramid.testing.setUp() self.config.include('pyramid_services') self.config.include('myapp.services')
def tearDown(self):
pyramid.testing.tearDown()
def test_db_maker(self):
result = self.config.find_service_factory(name='db')
self.assertEqual(result, dbsession_factory)
def test_login_factory(self):
result = self.config.find_service_factory(ILoginService)
self.assertEqual(result, login_factory)