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72 lines
2.9 KiB
72 lines
2.9 KiB
.. _tutorial-dbinit: |
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Step 4: Creating The Database |
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============================= |
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As outlined earlier, Flaskr is a database powered application, and more |
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precisely, it is an application powered by a relational database system. Such |
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systems need a schema that tells them how to store that information. So |
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before starting the server for the first time it's important to create |
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that schema. |
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Such a schema can be created by piping the `schema.sql` file into the |
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`sqlite3` command as follows:: |
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sqlite3 /tmp/flaskr.db < schema.sql |
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The downside of this is that it requires the sqlite3 command to be |
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installed which is not necessarily the case on every system. This also |
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requires that we provide the path to the database which can introduce |
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errors. It's a good idea to add a function that initializes the database |
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for you to the application. |
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To do this we can create a function and hook it into the ``flask`` command |
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that initializes the database. Let me show you the code first. Just add |
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this function below the `connect_db` function in `flaskr.py`:: |
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def init_db(): |
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db = get_db() |
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with app.open_resource('schema.sql', mode='r') as f: |
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db.cursor().executescript(f.read()) |
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db.commit() |
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@app.cli.command('initdb') |
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def initdb_command(): |
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"""Initializes the database.""" |
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init_db() |
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print 'Initialized the database.' |
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The ``app.cli.command()`` decorator registers a new command with the |
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``flask`` script. When the command executes Flask will automatically |
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create a application context for us bound to the right application. |
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Within the function we can then access :attr:`flask.g` and other things as |
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we would expect. When the script ends, the application context tears down |
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and the database connection is released. |
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We want to keep an actual functions around that initializes the database |
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though so that we can easily create databases in unittests later. (For |
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more information see :ref:`testing`.) |
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The :func:`~flask.Flask.open_resource` method of the application object |
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is a convenient helper function that will open a resource that the |
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application provides. This function opens a file from the resource |
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location (your `flaskr` folder) and allows you to read from it. We are |
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using this here to execute a script on the database connection. |
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The connection object provided by SQLite can give us a cursor object. |
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On that cursor there is a method to execute a complete script. Finally we |
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only have to commit the changes. SQLite 3 and other transactional |
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databases will not commit unless you explicitly tell it to. |
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Now it is possible to create a database with the ``flask`` script:: |
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flask --app=flaskr initdb |
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Initialized the database. |
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.. admonition:: Troubleshooting |
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If you get an exception later that a table cannot be found check that |
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you did execute the `initdb` command and that your table names are |
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correct (singular vs. plural for example). |
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Continue with :ref:`tutorial-views`
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