Remove "unique" constraint for part / order relationship

InvenTree/order/migrations/0043_auto_20210330_0013.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.0.7 on 2021-03-29 13:13
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0042_auto_20210310_1619'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='salesorderlineitem',
+            unique_together=set(),
+        ),
+    ]

InvenTree/order/models.py

@@ -663,7 +663,6 @@ class SalesOrderLineItem(OrderLineItem):
 
     class Meta:
         unique_together = [
-            ('order', 'part'),
         ]
 
     def fulfilled_quantity(self):