Add depends_on relation on orders

uncloud_pay/migrations/0013_auto_20200508_1446.py

@@ -0,0 +1,24 @@
+# Generated by Django 3.0.6 on 2020-05-08 14:46
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('uncloud_pay', '0012_billnico'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='order',
+            name='depends_on',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='parent_of', to='uncloud_pay.Order'),
+        ),
+        migrations.AlterField(
+            model_name='order',
+            name='replaced_by',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='supersede', to='uncloud_pay.Order'),
+        ),
+    ]