Custom migration to find BomItem / BuildItem links where they exist

InvenTree/build/migrations/0029_auto_20210601_1525.py

@@ -0,0 +1,62 @@
+# Generated by Django 3.2 on 2021-06-01 05:25
+
+from django.db import migrations
+
+
+def assign_bom_items(apps, schema_editor):
+    """
+    Run through existing BuildItem objects,
+    and assign a matching BomItem
+    """
+
+    BuildItem = apps.get_model('build', 'builditem')
+    BomItem = apps.get_model('part', 'bomitem')
+    Part = apps.get_model('part', 'part')
+    
+    print("Assigning BomItems to existing BuildItem objects")
+
+    count_valid = 0
+    count_total = 0
+
+    for build_item in BuildItem.objects.all():
+
+        # Try to find a BomItem which matches the BuildItem
+        # Note: Before this migration, variant stock assignment was not allowed,
+        #       so BomItem lookup should be pretty easy
+
+        count_total += 1
+
+        try:
+            bom_item = BomItem.objects.get(
+                part__id=build_item.build.part.pk,
+                sub_part__id=build_item.stock_item.part.pk,
+            )
+
+            build_item.bom_item = bom_item
+            build_item.save()
+
+            count_valid += 1
+
+        except BomItem.DoesNotExist:
+            pass
+
+    print(f"Assigned BomItem for {count_valid}/{count_total} entries")
+
+
+def unassign_bom_items(apps, schema_editor):
+    """
+    Reverse migration does not do anything.
+    Function here to preserve ability to reverse migration
+    """
+    pass
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0028_builditem_bom_item'),
+    ]
+
+    operations = [
+        migrations.RunPython(assign_bom_items, reverse_code=unassign_bom_items),
+    ]