How to Migrate Models Between Django Apps in Django 1.7?

Practical Guide to Migrating Models Between Django Apps in Django 1.7

Background

As a Django developer progresses, refactoring project structure often becomes necessary to improve organization and maintainability. This includes moving models to their own individual apps for better encapsulation. However, this process can be daunting in earlier Django versions due to the challenges of dealing with foreign keys.

Solution for Django 1.7 and Later

With the introduction of migrations in Django 1.7, migrating models between apps has become more manageable. The SeparateDatabaseAndState operation allows us to rename a model table concurrently while updating its state in multiple apps.

Step-by-Step Instructions

Removing the Model from the Old App

1. Create an empty migration for the old app:

<code class="python">python manage.py makemigrations old_app --empty</code>

2. In the migration file, define the RenameTable, DeleteModel, and SeparateDatabaseAndState operations:

<code class="python">class Migration(migrations.Migration):

    dependencies = []

    database_operations = [
        migrations.RenameModel('TheModel', 'newapp_themodel')
    ]

    state_operations = [
        migrations.DeleteModel('TheModel')
    ]

    operations = [
        migrations.SeparateDatabaseAndState(
            database_operations=database_operations,
            state_operations=state_operations)
    ]</code>

Adding the Model to the New App

1. Copy the model to the new app's model.py.
2. Run the makemigrations command for the new app:

<code class="python">python manage.py makemigrations new_app</code>

3. In the migration file, wrap the CreateModel operation within a SeparateDatabaseAndState operation to prevent table recreation:

<code class="python">class Migration(migrations.Migration):

    dependencies = [
        ('old_app', 'above_migration')
    ]

    state_operations = [
        migrations.CreateModel(
            name='TheModel',
            fields=[
                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
            ],
            options={
                'db_table': 'newapp_themodel',
            },
            bases=(models.Model,),
        )
    ]

    operations = [
        migrations.SeparateDatabaseAndState(state_operations=state_operations)
    ]</code>

By following these steps, you can successfully migrate models between apps in Django 1.7 and later, ensuring a clean and maintainable project structure.

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