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.. _developers-extensions:
Extensions
==========
What are extension and what is their purpose? Small piece of code that
should ease the integration of a third party library. As such many of
extensions have been already developed and one can find them in the
`Flask Extension Registry`_. Everyone should check first if there is
a usable extensions before developing new one according to
`Flask Extension Development`_ guideline that will help you get your
extension running.
.. _Flask Extension Registry: http://flask.pocoo.org/extensions/
.. _Flask Extension Development: http://flask.pocoo.org/docs/extensiondev/
Pluging an Existing Extension
-----------------------------
Extensions are all located in a package called ``flask_something``
where "something" is the name of the extension you want to bridge.
So for example if you plan to add support for an extension named
`login`, you would name your extension's package ``invenio.ext.login``.
Alternatively, if the extension reads only configuration from
``current_app.config``, you can just list in ``EXTENSIONS`` option
as ``flask.ext.something:Something``, where ``Something`` has to accept
application object as first argument::
class Something(object):
def __init__(self, app, optional=None):
pass
But how do extensions look like themselves? An extension has to ensure
that it works with multiple Flask application instances at once.
Code structure
--------------
So let's get started with creating such a extension bridge. The bridge
we want to create here will provide very basic support for `Flask Login`_.
First we create the following folder structure::
invenio/ext/login/
__init__.py
legacy_user.py
README
Here's the contents of the most important files:
* ``__init__.py`` contains :func:`~invenio.ext.login.setup_app` function::
from .legacy_user import UserInfo
def setup_app(app):
"""Setup login extension."""
# Let's create login manager.
_login_manager = LoginManager(app)
_login_manager.login_view = app.config.get('CFG_LOGIN_VIEW',
'webaccount.login')
_login_manager.anonymous_user = UserInfo
@_login_manager.user_loader
def _load_user(uid):
"""
Function should not raise an exception if uid is not valid
or User was not found in database.
"""
return UserInfo(int(uid))
return app
* ``legacy_user.py`` contains implementation ``UserMixin`` object::
from flask.ext.login import UserMixin
from werkzeug.datastructures import CallbackDict, CombinedMultiDict
class UserInfo(CombinedMultiDict, UserMixin):
"""
This provides legacy implementations for the methods that Flask-Login
and Invenio 1.x expects user objects to have.
"""
def __init__(self, uid=None, force=False):
...
.. _Flask Login: https://flask-login.readthedocs.org/en/latest/
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