Fix BuildItem with empty BuildLine reference (#7178)

src/backend/InvenTree/build/migrations/0049_alter_builditem_build_line.py

@@ -0,0 +1,19 @@
+# Generated by Django 4.2.12 on 2024-05-08 01:38
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0048_build_project_code'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='builditem',
+            name='build_line',
+            field=models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='allocations', to='build.buildline'),
+        ),
+    ]

src/backend/InvenTree/build/migrations/0050_auto_20240508_0138.py

@@ -0,0 +1,26 @@
+# Generated by Django 4.2.12 on 2024-05-08 01:38
+
+from django.db import migrations
+
+
+def forward(apps, schema_editor):
+    """Find and delete any BuildItem instances which have a null BuildLine field."""
+    
+    BuildItem = apps.get_model('build', 'BuildItem')
+
+    items = BuildItem.objects.filter(build_line=None)
+
+    if items.count() > 0:
+        print(f"Deleting {items.count()} BuildItem objects with null BuildLine field")
+        items.delete()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0049_alter_builditem_build_line'),
+    ]
+
+    operations = [
+        migrations.RunPython(forward, reverse_code=migrations.RunPython.noop),
+    ]

src/backend/InvenTree/build/models.py

@@ -1569,7 +1569,7 @@ class BuildItem(InvenTree.models.InvenTreeMetadataModel):
 
     build_line = models.ForeignKey(
         BuildLine,
-        on_delete=models.SET_NULL, null=True,
+        on_delete=models.CASCADE, null=True,
         related_name='allocations',
     )