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    <p>To build on <a href="https://stackoverflow.com/users/215414/potr-czachur">Potr Czachur</a>'s <a href="https://stackoverflow.com/a/1770138/305736">answer</a>, situations that involve ForeignKeys are more complicated and should be handled slightly differently.</p> <p>(The following example builds on the <code>common</code> and <code>specific</code> apps referred to the in the current answer).</p> <pre><code># common/models.py class Cat(models.Model): # ... class Toy(models.Model): belongs_to = models.ForeignKey(Cat) # ... </code></pre> <p>would then change to</p> <pre><code># common/models.py from specific.models import Cat class Toy(models.Model): belongs_to = models.ForeignKey(Cat) # ... # specific/models.py class Cat(models.Model): # ... </code></pre> <p>Running</p> <pre><code>./manage.py schemamigration common --auto ./manage.py schemamigration specific --auto # or --initial </code></pre> <p>would generate the following the migrations (I'm intentionally ignoring Django ContentType changes—see previously referenced answer for how to handle that):</p> <pre><code># common/migrations/0009_auto__del_cat.py class Migration(SchemaMigration): def forwards(self, orm): db.delete_table('common_cat') db.alter_column('common_toy', 'belongs_to_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['specific.Cat'])) def backwards(self, orm): db.create_table('common_cat', ( # ... )) db.alter_column('common_toy', 'belongs_to_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['common.Cat'])) # specific/migrations/0004_auto__add_cat.py class Migration(SchemaMigration): def forwards(self, orm): db.create_table('specific_cat', ( # ... )) def backwards(self, orm): db.delete_table('specific_cat') </code></pre> <p>As you can see, the FK must be altered to reference the new table. We need to add a dependency so that we know the order in which the migrations will be applied (and thus that the table will exist before we try to add a FK to it) but we also need to make sure rolling backwards works too because <strong>the dependency applies in the reverse direction</strong>.</p> <pre><code># common/migrations/0009_auto__del_cat.py class Migration(SchemaMigration): depends_on = ( ('specific', '0004_auto__add_cat'), ) def forwards(self, orm): db.alter_column('common_toy', 'belongs_to_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['specific.Cat'])) def backwards(self, orm): db.rename_table('specific_cat', 'common_cat') db.alter_column('common_toy', 'belongs_to_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['common.Cat'])) # specific/migrations/0004_auto__add_cat.py class Migration(SchemaMigration): def forwards(self, orm): db.rename_table('common_cat', 'specific_cat') def backwards(self, orm): pass </code></pre> <p>Per the <a href="http://south.readthedocs.org/en/latest/dependencies.html" rel="nofollow noreferrer">South documentation</a>, <code>depends_on</code> will ensure that <code>0004_auto__add_cat</code> runs before <code>0009_auto__del_cat</code> <strong>when migrating forwards</strong> but in the <strong>opposite order when migrating backwards</strong>. If we left <code>db.rename_table('specific_cat', 'common_cat')</code> in the <code>specific</code> rollback, the <code>common</code> rollback would fail when trying to migrate the ForeignKey because the table referenced table wouldn't exist.</p> <p>Hopefully this is closer to a "real world" situation than the existing solutions and someone will find this helpful. Cheers!</p>
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    1. USMatt Briançon
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