Cache A/B termination devices on the Cable model

netbox/dcim/migrations/0075_cable_devices.py

@@ -0,0 +1,46 @@
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+def cache_cable_devices(apps, schema_editor):
+    Cable = apps.get_model('dcim', 'Cable')
+
+    # Cache A/B termination devices on all existing Cables. Note that the custom save() method on Cable is not
+    # available during a migration, so we replicate its logic here.
+    for cable in Cable.objects.all():
+
+        termination_a_model = apps.get_model(cable.termination_a_type.app_label, cable.termination_a_type.model)
+        if hasattr(termination_a_model, 'device'):
+            termination_a = termination_a_model.objects.get(pk=cable.termination_a_id)
+            cable._termination_a_device = termination_a.device
+
+        termination_b_model = apps.get_model(cable.termination_b_type.app_label, cable.termination_b_type.model)
+        if hasattr(termination_b_model, 'device'):
+            termination_b = termination_b_model.objects.get(pk=cable.termination_b_id)
+            cable._termination_b_device = termination_b.device
+
+        cable.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('dcim', '0074_increase_field_length_platform_name_slug'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='cable',
+            name='_termination_a_device',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='dcim.Device'),
+        ),
+        migrations.AddField(
+            model_name='cable',
+            name='_termination_b_device',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='dcim.Device'),
+        ),
+        migrations.RunPython(
+            code=cache_cable_devices,
+            reverse_code=migrations.RunPython.noop
+        ),
+    ]