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74 lines
2.7 KiB
74 lines
2.7 KiB
15 years ago
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Application Factories
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=====================
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If you are already using packages and modules for your application
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(:ref:`packages`) there are couple of really nice ways to further improve
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the experience. A common pattern is creating the application object when
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the module is imported. But if you move the creation of this object,
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into a function, you can then create multiple instances of this and later.
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So why would you want to do this?
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1. Testing. You can have instances of the application with different
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settings to test every case.
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2. Multiple instances. Imagine you want to run different versions of the
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same application. Of course you could have multiple instances with
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different configs set up in your webserver, but if you use factories,
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you can have multiple instances of the same application running in the
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same application process which can be handy.
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So how would you then actually implement that?
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Basic Factories
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---------------
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The idea is to set up the application in a function. Like this::
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def create_app(config_filename):
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app = Flask(__name__)
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app.config.from_pyfile(config_filename)
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from yourapplication.views.admin import admin
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from yourapplication.views.frontend import frontend
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app.register_module(admin)
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app.register_module(frontend)
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return app
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The downside is that you cannot use the application object in the modules
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at import time. You can however use it from within a request. How do you
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get access the application with the config? Use
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:data:`~flask.current_app`::
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from flask import current_app, Module, render_template
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admin = Module(__name__, url_prefix='/admin')
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@admin.route('/')
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def index():
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return render_template(current_app.config['INDEX_TEMPLATE'])
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Here we look up the name of a template in the config.
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Using Applications
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------------------
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So to use such an application you then have to create the application
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first. Here an example `run.py` file that runs such an application::
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from yourapplication import create_app
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app = create_app('/path/to/config.cfg')
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app.run()
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Factory Improvements
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--------------------
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The factory function from above is not very clever so far, you can improve
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it. The following changes are straightforward and possible:
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1. make it possible to pass in configuration values for unittests so that
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you don't have to create config files on the filesystem
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2. call a function from a module when the application is setting up so
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that you have a place to modify attributes of the application (like
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hooking in before / after request handlers etc.)
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3. Add in WSGI middlewares when the application is creating if necessary.
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