Remove the problematic migration entirely

- The thumbnail check code is run every time the server is started anyway!

InvenTree/part/migrations/0034_auto_20200404_1238.py

@@ -1,32 +1,20 @@
 # Generated by Django 2.2.10 on 2020-04-04 12:38
 
 from django.db import migrations
-from django.db.utils import OperationalError, ProgrammingError
-
-from part.models import Part
-from stdimage.utils import render_variations
 
 
 def create_thumbnails(apps, schema_editor):
     """
     Create thumbnails for all existing Part images.
+
+    Note: This functionality is now performed in apps.py, 
+    as running the thumbnail script here caused too many database level errors.
+
+    This migration is left here to maintain the database migration history
+
     """
+    pass
 
-    try:
-        for part in Part.objects.all():
-            # Render thumbnail for each existing Part 
-            if part.image:
-                try:
-                    part.image.render_variations()
-                except FileNotFoundError:
-                    print("Missing image:", part.image())
-                    # The image is missing, so clear the field
-                    part.image = None
-                    part.save()
-                    
-    except (OperationalError, ProgrammingError):
-        # Migrations have not yet been applied - table does not exist
-        print("Could not generate Part thumbnails")
 
 class Migration(migrations.Migration):
 
@@ -35,5 +23,5 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
-        migrations.RunPython(create_thumbnails),
+        migrations.RunPython(create_thumbnails, reverse_code=create_thumbnails),
     ]