Remove unique-together requirement for BomItem model (#3104)

* Remove unique-together requirement for BomItem model

Ref: https://github.com/inventree/InvenTree/issues/1254

* Update unit test

* Remove unused import

InvenTree/part/migrations/0077_alter_bomitem_unique_together.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.2.13 on 2022-05-31 01:42
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0076_auto_20220516_0819'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='bomitem',
+            unique_together=set(),
+        ),
+    ]

InvenTree/part/models.py

@@ -2899,9 +2899,6 @@ class BomItem(models.Model, DataImportMixin):
     class Meta:
         verbose_name = _("BOM Item")
 
-        # Prevent duplication of parent/child rows
-        unique_together = ('part', 'sub_part')
-
     def __str__(self):
         return "{n} x {child} to make {parent}".format(
             parent=self.part.full_name,