using a separate field for a Product image's thumbnail

cash/admin.py

@@ -94,6 +94,7 @@ class ProductAdmin(admin.ModelAdmin):
 	list_filter = ['category', 'active']
 	ordering = ('-active', 'name')
 	inlines = [ProductBarcodeInline]
+	fields = ('name', 'price', 'active', 'category', 'image')
 
 class ProductCategoryAdmin(admin.ModelAdmin):
 	list_display = ('name', 'comment')

cash/models.py

@@ -1,14 +1,16 @@
 
 from django.conf import settings
 from django.db import models
+from django.core.files import File
 from django.contrib.auth.models import User
-from django.db.models.signals import post_save
+from django.db.models.signals import pre_save, post_save
 from django.db.models.signals import pre_delete
 from django.dispatch import receiver
 from django_auth_ldap.backend import populate_user
 from django.utils.translation import ugettext_lazy as _
 from django.utils.translation import ugettext_noop
 import PIL
+import StringIO
 
 class Account(models.Model):
 	user = models.OneToOneField(User)
@@ -114,6 +116,9 @@ class Product(models.Model):
 	                             verbose_name = _('category'))
 	image = models.ImageField(upload_to="products", verbose_name = _('image'),
 	                          blank=True, null=True)
+	image_thumbnail = models.ImageField(upload_to="products_thumb",
+	                                    verbose_name = _('image'),
+	                                    blank=True, null=True)
 
 	def __unicode__(self):
 		return self.name
@@ -122,19 +127,20 @@ class Product(models.Model):
 		verbose_name = _('product')
 		verbose_name_plural = _('products')
 
-@receiver(post_save, sender=Product)
+@receiver(pre_save, sender=Product)
 def product_post_save_handler(sender, instance, **kwargs):
 	img = instance.image
 	if img:
+		scaledFile = StringIO.StringIO()
 		img.open(mode='r')
 		with img:
 			scaled = PIL.Image.open(img)
 			thumbnail_size = getattr(settings, 'THUMBNAIL_SIZE', (150, 150))
 			scaled.thumbnail(thumbnail_size, PIL.Image.ANTIALIAS)
+			scaled.save(scaledFile, 'PNG')
+		scaledFile.seek(0)
 
-		img.open(mode='w')
-		with img:
-			scaled.save(img)
+		instance.image_thumbnail.save(img.url, File(scaledFile), save=False)
 
 
 class ProductBarcode(models.Model):