Mickaël Mickaël - 7 months ago 14
Python Question

Loading initial data with Django 1.7 and data migrations

I recently switched from Django 1.6 to 1.7, and I began using migrations (I never used South).

Before 1.7, I used to load initial data with a

fixture/initial_data.json
file, which was loaded with the
python manage.py syncdb
command (when creating the database).

Now, I started using migrations, and this behavior is deprecated :


If an application uses migrations, there is no automatic loading of fixtures.
Since migrations will be required for applications in Django 2.0, this behavior is considered deprecated. If you want to load initial data for an app, consider doing it in a data migration.
(https://docs.djangoproject.com/en/1.7/howto/initial-data/#automatically-loading-initial-data-fixtures)


The official documentation does not have a clear example on how to do it, so my question is :

What is the best way to import such initial data using data migrations :


  1. Write Python code with multiple calls to
    mymodel.create(...)
    ,

  2. Use or write a Django function (like calling
    loaddata
    ) to load data from a JSON fixture file.



I prefer the second option.

I don't want to use South, as Django seems to be able to do it natively now.

Answer

Assuming you have a fixture file in <yourapp>/fixtures/initial_data.json

  1. Create your empty migration:

    In Django 1.7:

    python manage.py makemigrations --empty <yourapp>
    

    In Django 1.8+, you can provide a name:

    python manage.py makemigrations --empty <yourapp> --name load_intial_data
    
  2. Edit your migration file <yourapp>/migrations/0002_auto_xxx.py

    2.1. Custom implementation, inspired by Django' loaddata (initial answer):

    import os
    from sys import path
    from django.core import serializers
    
    fixture_dir = os.path.abspath(os.path.join(os.path.dirname(__file__), '../fixtures'))
    fixture_filename = 'initial_data.json'
    
    def load_fixture(apps, schema_editor):
        fixture_file = os.path.join(fixture_dir, fixture_filename)
    
        fixture = open(fixture_file, 'rb')
        objects = serializers.deserialize('json', fixture, ignorenonexistent=True)
        for obj in objects:
            obj.save()
        fixture.close()
    
    def unload_fixture(apps, schema_editor):
        "Brutally deleting all entries for this model..."
    
        MyModel = apps.get_model("yourapp", "ModelName")
        MyModel.objects.all().delete()
    
    class Migration(migrations.Migration):  
    
        dependencies = [
            ('yourapp', '0001_initial'),
        ]
    
        operations = [
            migrations.RunPython(load_fixture, reverse_code=unload_fixture),
        ]
    

    2.2. A simpler solution for load_fixture (per @juliocesar's suggestion):

    from django.core.management import call_command
    
    fixture_dir = os.path.abspath(os.path.join(os.path.dirname(__file__), '../fixtures'))
    fixture_filename = 'initial_data.json'
    
    def load_fixture(apps, schema_editor):
        fixture_file = os.path.join(fixture_dir, fixture_filename)
        call_command('loaddata', fixture_file) 
    

    Useful if you want to use a custom directory.

    2.3. Simplest: calling loaddata with app_label will load fixtures from the <yourapp>'s fixtures dir automatically :

    from django.core.management import call_command
    
    fixture = 'initial_data'
    
    def load_fixture(apps, schema_editor):
        call_command('loaddata', fixture, app_label='yourapp') 
    

    If you don't specify app_label, loaddata will try to load fixture filename from all apps fixtures directories (which you probably don't want).

  3. Run it

    python manage.py migrate <yourapp>