mirror of https://github.com/mitsuhiko/flask.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
72 lines
2.9 KiB
72 lines
2.9 KiB
.. _tutorial-dbinit: |
|
|
|
Step 4: Creating The Database |
|
============================= |
|
|
|
As outlined earlier, Flaskr is a database powered application, and more |
|
precisely, it is an application powered by a relational database system. Such |
|
systems need a schema that tells them how to store that information. So |
|
before starting the server for the first time it's important to create |
|
that schema. |
|
|
|
Such a schema can be created by piping the `schema.sql` file into the |
|
`sqlite3` command as follows:: |
|
|
|
sqlite3 /tmp/flaskr.db < schema.sql |
|
|
|
The downside of this is that it requires the sqlite3 command to be |
|
installed which is not necessarily the case on every system. This also |
|
requires that we provide the path to the database which can introduce |
|
errors. It's a good idea to add a function that initializes the database |
|
for you to the application. |
|
|
|
To do this we can create a function and hook it into the :command:`flask` command |
|
that initializes the database. Let me show you the code first. Just add |
|
this function below the `connect_db` function in :file:`flaskr.py`:: |
|
|
|
def init_db(): |
|
db = get_db() |
|
with app.open_resource('schema.sql', mode='r') as f: |
|
db.cursor().executescript(f.read()) |
|
db.commit() |
|
|
|
@app.cli.command('initdb') |
|
def initdb_command(): |
|
"""Initializes the database.""" |
|
init_db() |
|
print 'Initialized the database.' |
|
|
|
The ``app.cli.command()`` decorator registers a new command with the |
|
:command:`flask` script. When the command executes Flask will automatically |
|
create a application context for us bound to the right application. |
|
Within the function we can then access :attr:`flask.g` and other things as |
|
we would expect. When the script ends, the application context tears down |
|
and the database connection is released. |
|
|
|
We want to keep an actual functions around that initializes the database |
|
though so that we can easily create databases in unittests later. (For |
|
more information see :ref:`testing`.) |
|
|
|
The :func:`~flask.Flask.open_resource` method of the application object |
|
is a convenient helper function that will open a resource that the |
|
application provides. This function opens a file from the resource |
|
location (your `flaskr` folder) and allows you to read from it. We are |
|
using this here to execute a script on the database connection. |
|
|
|
The connection object provided by SQLite can give us a cursor object. |
|
On that cursor there is a method to execute a complete script. Finally we |
|
only have to commit the changes. SQLite 3 and other transactional |
|
databases will not commit unless you explicitly tell it to. |
|
|
|
Now it is possible to create a database with the :command:`flask` script:: |
|
|
|
flask --app=flaskr initdb |
|
Initialized the database. |
|
|
|
.. admonition:: Troubleshooting |
|
|
|
If you get an exception later that a table cannot be found check that |
|
you did execute the `initdb` command and that your table names are |
|
correct (singular vs. plural for example). |
|
|
|
Continue with :ref:`tutorial-views`
|
|
|