Fixtures

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What is a fixture?

A fixture is a collection of files that contain the serialized contents of the database. Each fixture has a unique name, and the files that comprise the fixture can be distributed over multiple directories, in multiple applications.

How to produce a fixture?

Fixtures can be generated by manage.py dumpdata. It’s also possible to generate custom fixtures by directly using serialization tools or even by handwriting them.

How to use a fixture?

Fixtures can be used to pre-populate database with data for tests:

class MyTestCase(TestCase):
    fixtures = ["fixture-label"]

or to provide some initial data using the loaddata command:

django-admin loaddata <fixture label>

Where Django looks for fixtures?

Django will search in these locations for fixtures:

  1. In the fixtures directory of every installed application
  2. In any directory listed in the FIXTURE_DIRS setting
  3. In the literal path named by the fixture

Django will load any and all fixtures it finds in these locations that match the provided fixture names. If the named fixture has a file extension, only fixtures of that type will be loaded. For example:

django-admin loaddata mydata.json

would only load JSON fixtures called mydata. The fixture extension must correspond to the registered name of a serializer (e.g., json or xml).

If you omit the extensions, Django will search all available fixture types for a matching fixture. For example:

django-admin loaddata mydata

would look for any fixture of any fixture type called mydata. If a fixture directory contained mydata.json, that fixture would be loaded as a JSON fixture.

The fixtures that are named can include directory components. These directories will be included in the search path. For example:

django-admin loaddata foo/bar/mydata.json

would search <app_label>/fixtures/foo/bar/mydata.json for each installed application, <dirname>/foo/bar/mydata.json for each directory in FIXTURE_DIRS, and the literal path foo/bar/mydata.json.

Fixtures loading order

Multiple fixtures can be specified in the same invocation. For example:

django-admin loaddata mammals birds insects

or in a test case class:

class AnimalTestCase(TestCase):
    fixtures = ["mammals", "birds", "insects"]

The order in which fixtures are loaded follows the order in which they are listed, whether it’s when using the management command or when listing them in the test case class as shown above.

In these examples, all the fixtures named mammals from all applications (in the order in which applications are defined in INSTALLED_APPS) will be loaded first. Subsequently, all the birds fixtures will be loaded, followed by all the insects fixtures.

Be aware that if the database backend supports row-level constraints, these constraints will be checked at the end of the transaction. Any relationships across fixtures may result in a load error if the database configuration does not support deferred constraint checking (refer to the MySQL docs for an example).

How fixtures are saved to the database?

When fixture files are processed, the data is saved to the database as is. Model defined save() methods are not called, and any pre_save or post_save signals will be called with raw=True since the instance only contains attributes that are local to the model. You may, for example, want to disable handlers that access related fields that aren’t present during fixture loading and would otherwise raise an exception:

from django.db.models.signals import post_save
from .models import MyModel


def my_handler(**kwargs):
    # disable the handler during fixture loading
    if kwargs["raw"]:
        return
    ...


post_save.connect(my_handler, sender=MyModel)

You could also write a decorator to encapsulate this logic:

from functools import wraps


def disable_for_loaddata(signal_handler):
    """
    Decorator that turns off signal handlers when loading fixture data.
    """

    @wraps(signal_handler)
    def wrapper(*args, **kwargs):
        if kwargs["raw"]:
            return
        signal_handler(*args, **kwargs)

    return wrapper


@disable_for_loaddata
def my_handler(**kwargs):
    ...

Just be aware that this logic will disable the signals whenever fixtures are deserialized, not just during loaddata.

Compressed fixtures

Fixtures may be compressed in zip, gz, bz2, lzma, or xz format. For example:

django-admin loaddata mydata.json

would look for any of mydata.json, mydata.json.zip, mydata.json.gz, mydata.json.bz2, mydata.json.lzma, or mydata.json.xz. The first file contained within a compressed archive is used.

Note that if two fixtures with the same name but different fixture type are discovered (for example, if mydata.json and mydata.xml.gz were found in the same fixture directory), fixture installation will be aborted, and any data installed in the call to loaddata will be removed from the database.

MySQL with MyISAM and fixtures

The MyISAM storage engine of MySQL doesn’t support transactions or constraints, so if you use MyISAM, you won’t get validation of fixture data, or a rollback if multiple transaction files are found.

Database-specific fixtures

If you’re in a multi-database setup, you might have fixture data that you want to load onto one database, but not onto another. In this situation, you can add a database identifier into the names of your fixtures.

For example, if your DATABASES setting has a users database defined, name the fixture mydata.users.json or mydata.users.json.gz and the fixture will only be loaded when you specify you want to load data into the users database.

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