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183 lines
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183 lines
7.1 KiB
Plaintext
=================================
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Providing initial data for models
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=================================
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It's sometimes useful to pre-populate your database with hard-coded data when
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you're first setting up an app. There's a couple of ways you can have Django
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automatically create this data: you can provide `initial data via fixtures`_, or
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you can provide `initial data as SQL`_.
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In general, using a fixture is a cleaner method since it's database-agnostic,
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but initial SQL is also quite a bit more flexible.
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.. _initial data as sql: `providing initial sql data`_
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.. _initial data via fixtures: `providing initial data with fixtures`_
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.. _initial-data-via-fixtures:
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Providing initial data with fixtures
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====================================
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A fixture is a collection of data that Django knows how to import into a
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database. The most straightforward way of creating a fixture if you've already
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got some data is to use the :djadmin:`manage.py dumpdata <dumpdata>` command.
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Or, you can write fixtures by hand; fixtures can be written as JSON, XML or YAML
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(with PyYAML_ installed) documents. The :doc:`serialization documentation
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</topics/serialization>` has more details about each of these supported
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:ref:`serialization formats <serialization-formats>`.
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.. _PyYAML: http://www.pyyaml.org/
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As an example, though, here's what a fixture for a simple ``Person`` model might
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look like in JSON:
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.. code-block:: js
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[
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{
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"model": "myapp.person",
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"pk": 1,
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"fields": {
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"first_name": "John",
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"last_name": "Lennon"
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}
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},
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{
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"model": "myapp.person",
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"pk": 2,
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"fields": {
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"first_name": "Paul",
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"last_name": "McCartney"
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}
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}
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]
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And here's that same fixture as YAML:
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.. code-block:: none
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- model: myapp.person
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pk: 1
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fields:
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first_name: John
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last_name: Lennon
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- model: myapp.person
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pk: 2
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fields:
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first_name: Paul
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last_name: McCartney
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You'll store this data in a ``fixtures`` directory inside your app.
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Loading data is easy: just call :djadmin:`manage.py loaddata <loaddata>`
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``<fixturename>``, where ``<fixturename>`` is the name of the fixture file
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you've created. Each time you run :djadmin:`loaddata`, the data will be read
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from the fixture and re-loaded into the database. Note this means that if you
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change one of the rows created by a fixture and then run :djadmin:`loaddata`
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again, you'll wipe out any changes you've made.
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Automatically loading initial data fixtures
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-------------------------------------------
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.. deprecated:: 1.7
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If an application uses migrations, there is no automatic loading of
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fixtures. Since migrations will be required for applications in Django 2.0,
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this behavior is considered deprecated. If you want to load initial data
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for an app, consider doing it in a :ref:`data migration <data-migrations>`.
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If you create a fixture named ``initial_data.[xml/yaml/json]``, that fixture will
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be loaded every time you run :djadmin:`migrate`. This is extremely convenient,
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but be careful: remember that the data will be refreshed *every time* you run
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:djadmin:`migrate`. So don't use ``initial_data`` for data you'll want to edit.
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Where Django finds fixture files
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--------------------------------
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By default, Django looks in the ``fixtures`` directory inside each app for
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fixtures. You can set the :setting:`FIXTURE_DIRS` setting to a list of
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additional directories where Django should look.
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When running :djadmin:`manage.py loaddata <loaddata>`, you can also
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specify a path to a fixture file, which overrides searching the usual
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directories.
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.. seealso::
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Fixtures are also used by the :ref:`testing framework
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<topics-testing-fixtures>` to help set up a consistent test environment.
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.. _initial-sql:
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Providing initial SQL data
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==========================
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.. deprecated:: 1.7
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If an application uses migrations, there is no loading of initial SQL data
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(including backend-specific SQL data). Since migrations will be required
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for applications in Django 2.0, this behavior is considered deprecated.
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If you want to use initial SQL for an app, consider doing it in a
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:ref:`data migration <data-migrations>`.
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Django provides a hook for passing the database arbitrary SQL that's executed
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just after the CREATE TABLE statements when you run :djadmin:`migrate`. You can
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use this hook to populate default records, or you could also create SQL
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functions, views, triggers, etc.
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The hook is simple: Django just looks for a file called ``sql/<modelname>.sql``,
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in your app directory, where ``<modelname>`` is the model's name in lowercase.
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So, if you had a ``Person`` model in an app called ``myapp``, you could add
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arbitrary SQL to the file ``sql/person.sql`` inside your ``myapp`` directory.
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Here's an example of what the file might contain:
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.. code-block:: sql
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INSERT INTO myapp_person (first_name, last_name) VALUES ('John', 'Lennon');
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INSERT INTO myapp_person (first_name, last_name) VALUES ('Paul', 'McCartney');
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Each SQL file, if given, is expected to contain valid SQL statements
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which will insert the desired data (e.g., properly-formatted
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``INSERT`` statements separated by semicolons).
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The SQL files are read by the :djadmin:`sqlcustom` and :djadmin:`sqlall`
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commands in :doc:`manage.py </ref/django-admin>`. Refer to the :doc:`manage.py
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documentation </ref/django-admin>` for more information.
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Note that if you have multiple SQL data files, there's no guarantee of
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the order in which they're executed. The only thing you can assume is
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that, by the time your custom data files are executed, all the
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database tables already will have been created.
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.. admonition:: Initial SQL data and testing
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This technique *cannot* be used to provide initial data for
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testing purposes. Django's test framework flushes the contents of
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the test database after each test; as a result, any data added
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using the custom SQL hook will be lost.
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If you require data for a test case, you should add it using
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either a :ref:`test fixture <topics-testing-fixtures>`, or
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programmatically add it during the ``setUp()`` of your test case.
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Database-backend-specific SQL data
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----------------------------------
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There's also a hook for backend-specific SQL data. For example, you
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can have separate initial-data files for PostgreSQL and SQLite. For
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each app, Django looks for a file called
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``<app_label>/sql/<modelname>.<backend>.sql``, where ``<app_label>`` is
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your app directory, ``<modelname>`` is the model's name in lowercase
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and ``<backend>`` is the last part of the module name provided for the
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:setting:`ENGINE <DATABASE-ENGINE>` in your settings file (e.g., if you have
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defined a database with an :setting:`ENGINE <DATABASE-ENGINE>` value of
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``django.db.backends.sqlite3``, Django will look for
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``<app_label>/sql/<modelname>.sqlite3.sql``).
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Backend-specific SQL data is executed before non-backend-specific SQL
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data. For example, if your app contains the files ``sql/person.sql``
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and ``sql/person.sqlite3.sql`` and you're installing the app on
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SQLite, Django will execute the contents of
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``sql/person.sqlite3.sql`` first, then ``sql/person.sql``.
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