Data Migration from Fixture

[Eugene]

Providing data via fixtures has been deprecated. In the past, we used to execute the loaddata manually. After Django introduce migration, the recommended way to import data is to create an empty migration and use RunPython migration operations to load the data.

This is a very common use case for data migration via fixture. We create the function just to call_command loaddata. ​http://stackoverflow.com/a/25981899/764592

In my opinion, instead of having to create the function, we can actually simplify this into a migration operation on its own.

As follow:

# Module: django.db.migrations.operations.base.special
from django.core.management import call_command                                 
class LoadFixture(Operation):                                                   
    reduces_to_sql = False                                                      
    reversible = False                                                          
                                                                                
    def __init__(self, *fixtures):                                              
        self.fixtures = fixtures                                                
                                                                                
    def state_forwards(self, app_label, state):                                 
        pass                                                                    
                                                                                
    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        for fixture in self.fixtures:                                           
            call_command('loaddata', fixture, app_label=app_label)              
                                                                                
    def database_backwards(self, app_label, schema_editor, from_state, to_state):
        pass                                                                    
                                                                                
    def describe(self):                                                         
        return "Load Fixture Operation" 

The implication of LoadFixture operations can be shown in the following example:

Assuming we have the fixture in foobar/fixtures/book_data.json

# File: foobar/migrations/0002_auto_load_book.py
class Migration(migrations.Migration):
    dependencies = [
        ('foobar', '0001_initial'),
    ]
    operations = [
        migrations.LoadFixture('book_data'),
    ]

The migration script is now much simpler.

PS: This is my first time creating a ticket and involved in Django internal. Let me know if I should make a PR for this feature.