pyramid-services 2.2
A service layer abstraction for the Pyramid Web Framework.
License: MIT
Requires Python: >=3.3
Keywords: pyramid,services,service layer,ioc container

================
pyramid_services
================

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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.

Installation
============

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 .

Setup
=====

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.

Usage
=====

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)

Registering per-request services
--------------------------------

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)

Examples
========

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

  # myapp/interfaces.py

  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

  # myapp/services.py

  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

  # myapp/main.py

  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

  # myapp/views.py

  @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

  # myapp/services.py

  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

  # myapp/model.py

  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

  # myapp/main.py

  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

  # myapp/views.py

  @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.

Testing Examples
================

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

  # myapp/tests/test_integration.py

  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)


2.2 (2019-04-22)
================

- Depend on ``wired >= 0.2`` to use the new
  ``wired.ServiceContainer.register_singleton`` api.

2.1 (2018-08-03)
================

- Add a ``NewServiceContainer`` event that is emitted when the service
  container is created before any calls to ``request.find_service``.

2.0 (2018-08-03)
================

- Drop support for Python 2.7.

- Replace service lookup with https://wired.readthedocs.io under the hood.

- Fixes service lookup with custom contexts such that the context is passed
  through to nested service lookups.

1.1 (2017-05-31)
================

Features
--------

- If the ``iface`` is a class then it must be the exact class that was
  registered originally. Subclasses are not identified as implementing
  the same interface at this time due to internal limitations.

1.0 (2017-05-11)
================

Features
--------

- Allow the ``iface`` argument to be an arbitrary Python object / class.
  See https://github.com/mmerickel/pyramid_services/pull/10

Backward Incompatibilities
--------------------------

- Drop Python 2.6 and Python 3.3 support.

0.4 (2016-02-03)
================

Backward Incompatibilities
--------------------------

- Drop Python 3.2 support.

- Use the original service context interface as the cache key instead
  of the current context. This means the service will be properly created
  only once for any context satisfying the original interface.

  Previously, if you requested the same service from 2 different contexts
  in the same request you would receive 2 service objects, instead of
  a cached version of the original service, assuming the service was
  registered to satisfy both contexts.
  See https://github.com/mmerickel/pyramid_services/pull/12

0.3 (2015-12-13)
================

- When using ``request.find_service`` during or before traversal the
  ``request.context`` is not valid. In these situations the ``context``
  parameter will default to ``None`` instead of raising an exception.
  See https://github.com/mmerickel/pyramid_services/pull/8

- Add ``config.find_service_factory`` and ``request.find_service_factory``.
  See https://github.com/mmerickel/pyramid_services/pull/4

0.2 (2015-03-13)
================

- Change ``find_service(..., context=None)`` to use a context of ``None``.
  Previously this would fallback to using ``request.context`` if the
  ``context`` was ``None``. Now ``find_service`` will only fallback to
  ``request.context`` when no ``context`` argument is specified.
  See https://github.com/mmerickel/pyramid_services/pull/3

- Support ``introspectable`` for services so that they show up in the
  pyramid_debugtoolbar and elsewhere.
  See https://github.com/mmerickel/pyramid_services/pull/2

0.1.1 (2015-02-17)
==================

- Support for ``request.find_service``, ``config.register_service``, and
  ``config.register_service_factory``.
- Initial commits.