feat: field pre_purchase_order_id for purchase_order (allow null)

business/migrations/0027_purchaseorder_from_pre_purchase.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('business', '0026_salesorder_from_pre_sales_order'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='purchaseorder',
+            name='from_pre_purchase_order_id',
+            field=models.BigIntegerField(blank=True, null=True, verbose_name='关联预采购单ID'),
+        ),
+    ]