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.
80 lines
3.1 KiB
80 lines
3.1 KiB
.. _tutorial-dbinit: |
|
|
|
Step 5: 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. |
|
Before starting the server for the first time, it's important to create |
|
that schema. |
|
|
|
Such a schema could be created by piping the ``schema.sql`` file into the |
|
``sqlite3`` command as follows:: |
|
|
|
sqlite3 /tmp/flaskr.db < schema.sql |
|
|
|
However, 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 you provide the path to the database, which can introduce |
|
errors. |
|
|
|
Instead of the ``sqlite3`` command above, it's a good idea to add a function |
|
to our application that initializes the database for you. To do this, you |
|
can create a function and hook it into a :command:`flask` command that |
|
initializes the database. |
|
|
|
Take a look at the code segment below. A good place to add this function, |
|
and command, is just 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 an application context which is bound to the right application. |
|
Within the function, you can then access :attr:`flask.g` and other things as |
|
you might expect. When the script ends, the application context tears down |
|
and the database connection is released. |
|
|
|
You will want to keep an actual function around that initializes the database, |
|
though, so that we can easily create databases in unit tests later on. (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 (the :file:`flaskr/flaskr` folder) and allows you to read from it. |
|
It is used in this example to execute a script on the database connection. |
|
|
|
The connection object provided by SQLite can give you a cursor object. |
|
On that cursor, there is a method to execute a complete script. Finally, you |
|
only have to commit the changes. SQLite3 and other transactional |
|
databases will not commit unless you explicitly tell it to. |
|
|
|
Now, in a terminal, from the application root directory :file:`flaskr/` it is |
|
possible to create a database with the :command:`flask` script:: |
|
|
|
flask initdb |
|
Initialized the database. |
|
|
|
.. admonition:: Troubleshooting |
|
|
|
If you get an exception later on stating 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`
|
|
|