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Added appfactory pattern

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1 parent 182ee31 commit 02b916d509422a4703df5110110686288666d3d5 @mitsuhiko committed
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  1. +73 −0 docs/patterns/appfactories.rst
  2. +1 −0  docs/patterns/index.rst
73 docs/patterns/appfactories.rst
@@ -0,0 +1,73 @@
+Application Factories
+If you are already using packages and modules for your application
+(:ref:`packages`) there are couple of really nice ways to further improve
+the experience. A common pattern is creating the application object when
+the module is imported. But if you move the creation of this object,
+into a function, you can then create multiple instances of this and later.
+So why would you want to do this?
+1. Testing. You can have instances of the application with different
+ settings to test every case.
+2. Multiple instances. Imagine you want to run different versions of the
+ same application. Of course you could have multiple instances with
+ different configs set up in your webserver, but if you use factories,
+ you can have multiple instances of the same application running in the
+ same application process which can be handy.
+So how would you then actually implement that?
+Basic Factories
+The idea is to set up the application in a function. Like this::
+ def create_app(config_filename):
+ app = Flask(__name__)
+ app.config.from_pyfile(config_filename)
+ from yourapplication.views.admin import admin
+ from yourapplication.views.frontend import frontend
+ app.register_module(admin)
+ app.register_module(frontend)
+ return app
+The downside is that you cannot use the application object in the modules
+at import time. You can however use it from within a request. How do you
+get access the application with the config? Use
+ from flask import current_app, Module, render_template
+ admin = Module(__name__, url_prefix='/admin')
+ @admin.route('/')
+ def index():
+ return render_template(current_app.config['INDEX_TEMPLATE'])
+Here we look up the name of a template in the config.
+Using Applications
+So to use such an application you then have to create the application
+first. Here an example `` file that runs such an application::
+ from yourapplication import create_app
+ app = create_app('/path/to/config.cfg')
+Factory Improvements
+The factory function from above is not very clever so far, you can improve
+it. The following changes are straightforward and possible:
+1. make it possible to pass in configuration values for unittests so that
+ you don't have to create config files on the filesystem
+2. call a function from a module when the application is setting up so
+ that you have a place to modify attributes of the application (like
+ hooking in before / after request handlers etc.)
+3. Add in WSGI middlewares when the application is creating if necessary.
1  docs/patterns/index.rst
@@ -17,6 +17,7 @@ Snippet Archives <>`_.
:maxdepth: 2
+ appfactories

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