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75 lines
2.7 KiB
75 lines
2.7 KiB
.. _app-factories: |
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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 a 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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