Django function for loading fixtures which use the current migration state of the model

migration_loaddata.py

import os
import logging

from django.core import serializers

LOGGER = logging.getLogger(__name__)


def load_fixture(app, fixture, ignorenonexistent=True):
    """
    A factory to load a named fixture via a data migration.
    """

    def inner(apps, schema_editor):
        """
        Loads migrations that work at current state of a model, in constrast to
        `loaddata` which requires a fixture to have data matching the fields
        defined in `models.py`.

        Based on https://gist.github.com/leifdenby/4586e350586c014c1c9a
        """

        # relative path to fixtures
        fixtures_dir = os.path.join(app, 'fixtures')

        # monkey patch serializers `apps` so that it uses the models in the
        # current migration state
        original_apps = serializers.python.apps

        try:
            serializers.python.apps = apps

            objects = None

            for extension in ('json', 'yaml', 'xml'):
                fixture_path = os.path.join(
                    fixtures_dir,
                    '%s.%s' % (fixture, extension))

                LOGGER.debug("Trying %s", fixtures_dir)

                if os.path.exists(fixture_path):
                    print("Loading fixtures from %s... " % fixture_path)

                    with open(fixture_path, 'rb') as file_:
                        objects = serializers.deserialize(
                            extension, file_,
                            ignorenonexistent=ignorenonexistent)

                        count = 0
                        for obj in objects:
                            obj.save()
                            count += 1

                        print("Loaded %d objects." % count)

            if objects is None:
                raise Exception(
                    "Couldn't find the '%s' fixture for the '%s' app." % (
                        fixture, app))
        finally:
            serializers.python.apps = original_apps

    return inner

Thank you for modifying the original script. How should this be run from a migration file?

The objects are inserted but I get an error CommandError: Unknown command: None

This was my migration, perhaps you can advise how you run it?

def forwards_func(apps, schema_editor):
    command = load_fixture("users", "initial_data")
    management.call_command(command(apps, schema_editor), verbosity=0)

class Migration(migrations.Migration):

    dependencies = [
        ("users", "0001_initial"),
    ]

    operations = [
        migrations.RunPython(forwards_func, reverse_func),
    ]

Solved!

def forwards_func(apps, schema_editor):
    command = load_fixture("users", "initial_data")
    command(apps, schema_editor)

Designed as a factory so: `forwards_func = load_fixture(...)`

…

On 12 Sep 2020, 21:29 +1000, Ian Yardley ***@***.***>, wrote: @yardley commented on this gist. Solved! def forwards_func(apps, schema_editor): command = load_fixture("users", "initial_data") command(apps, schema_editor) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

I understand now, thank you.

operations = [
  migrations.RunPython(load_fixture("users", "initial_data"), reverse_func),
]

Using django-cookiecutter, since apps are inside project folder I needed to

operations = [
  migrations.RunPython(load_fixture("project_folder/name_app", "initial_data"), reverse_func),
]

This doesn't appear to handle auto increment sequences. Django's loaddata command does the following:

        if self.loaded_object_count > 0:
            sequence_sql = connection.ops.sequence_reset_sql(no_style(), self.models)
            if sequence_sql:
                with connection.cursor() as cursor:
                    for line in sequence_sql:
                        cursor.execute(line)

Without something like this anyone who uses this is going to run into primary key conflicts.