Require Build and StockItem to be unique_together in BuildItem class

InvenTree/build/migrations/0007_auto_20190429_2255.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2 on 2019-04-29 12:55
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0009_auto_20190428_0841'),
+        ('build', '0006_auto_20190429_2233'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='builditem',
+            unique_together={('build', 'stock_item')},
+        ),
+    ]