Fix migration

backend/api/migrations/0017_example_uuid.py

@@ -5,6 +5,13 @@ import uuid
 from django.db import migrations, models
 
 
+def create_uuid(apps, schema_editor):
+    Example = apps.get_model('api', 'example')
+    for example in Example.objects.all():
+        example.uuid = uuid.uuid4()
+        example.save()
+
+
 class Migration(migrations.Migration):
 
     dependencies = [
@@ -15,6 +22,12 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name="example",
             name="uuid",
-            field=models.UUIDField(db_index=True, default=uuid.uuid4, editable=False, unique=True),
+            field=models.UUIDField(editable=False, blank=True, null=True),
         ),
-    ]
+        migrations.RunPython(create_uuid),
+        migrations.AlterField(
+            model_name='example',
+            name='uuid',
+            field=models.UUIDField(db_index=True, unique=True)
+        )
+    ]