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56 lines
2.3 KiB
56 lines
2.3 KiB
.. _tutorial-dbcon: |
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Step 4: Request Database Connections |
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------------------------------------ |
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Now we know how we can open database connections and use them for scripts, |
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but how can we elegantly do that for requests? We will need the database |
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connection in all our functions so it makes sense to initialize them |
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before each request and shut them down afterwards. |
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Flask allows us to do that with the :meth:`~flask.Flask.before_request`, |
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:meth:`~flask.Flask.after_request` and :meth:`~flask.Flask.teardown_request` |
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decorators. In debug mode, if an error is raised, |
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:meth:`~flask.Flask.after_request` won't be run, and you'll have access to the |
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db connection in the interactive debugger:: |
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@app.before_request |
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def before_request(): |
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g.db = connect_db() |
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@app.after_request |
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def after_request(response): |
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g.db.close() |
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return response |
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If you want to guarantee that the connection is always closed in debug mode, you |
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can close it in a function decorated with :meth:`~flask.Flask.teardown_request`:: |
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@app.before_request |
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def before_request(): |
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g.db = connect_db() |
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@app.teardown_request |
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def teardown_request(exception): |
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g.db.close() |
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Functions marked with :meth:`~flask.Flask.before_request` are called before |
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a request and passed no arguments. Functions marked with |
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:meth:`~flask.Flask.after_request` are called after a request and |
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passed the response that will be sent to the client. They have to return |
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that response object or a different one. In this case we just return it |
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unchanged. |
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Functions marked with :meth:`~flask.Flask.teardown_request` get called after the |
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response has been constructed. They are not allowed to modify the request, and |
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their return values are ignored. If an exception occurred while the request was |
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being processed, it is passed to each function; otherwise, None is passed in. |
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We store our current database connection on the special :data:`~flask.g` |
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object that flask provides for us. This object stores information for one |
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request only and is available from within each function. Never store such |
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things on other objects because this would not work with threaded |
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environments. That special :data:`~flask.g` object does some magic behind |
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the scenes to ensure it does the right thing. |
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Continue to :ref:`tutorial-views`.
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