forked from orbit-oss/flask
8bb972e5ae
app.open_resource needs to get called with the correct mode param (python3 will read bytes [not str] if the wrong mode is used), add mode param docs. rv.data is bytes, fix the data type we compare it with to be also bytes
66 lines
2.6 KiB
ReStructuredText
66 lines
2.6 KiB
ReStructuredText
.. _tutorial-dbinit:
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Step 3: Creating The Database
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=============================
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Flaskr is a database powered application as outlined earlier, and more
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precisely, 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. Also one has
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to provide the path to the database there which leaves some place for
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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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If you want to do that, you first have to import the
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:func:`contextlib.closing` function from the contextlib package.
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Accordingly, add the following lines to your existing imports in `flaskr.py`::
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from contextlib import closing
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Next we can create a function called `init_db` that initializes the
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database. For this we can use the `connect_db` function we defined
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earlier. Just add that function below the `connect_db` function in
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`flaskr.py`::
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def init_db():
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with closing(connect_db()) as 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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The :func:`~contextlib.closing` helper function allows us to keep a
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connection open for the duration of the `with` block. The
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:func:`~flask.Flask.open_resource` method of the application object
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supports that functionality out of the box, so it can be used in the
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`with` block directly. 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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When we connect to a database we get a connection object (here called
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`db`) that can give us a cursor. On that cursor there is a method to
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execute a complete script. Finally we only have to commit the changes.
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SQLite 3 and other transactional databases will not commit unless you
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explicitly tell it to.
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Now it is possible to create a database by starting up a Python shell and
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importing and calling that function::
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>>> from flaskr import init_db
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>>> init_db()
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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 call the `init_db` function and that your table names are
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correct (singular vs. plural for example).
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Continue with :ref:`tutorial-dbcon`
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