Generate thumbnails when image is being saved

Too lax unique constraints for Thumbnail coped with "on demand" thumbnail
generation may leave database in inconsistent state where two thumbnail for
the same size are saved. We should be able to prevent that from happening
by generating all thumbnails when we save the image. Should fix #24, but
I can't figure out a way to actually test it.

pinry/core/api.py

@@ -59,7 +59,7 @@ class UserResource(ModelResource):
 
 def filter_generator_for(size):
     def wrapped_func(bundle, **kwargs):
-        return Thumbnail.objects.get_or_create_at_size(bundle.obj.pk, size, **kwargs)
+        return bundle.obj.get_by_size(size)
     return wrapped_func
 
 

pinry/core/models.py

@@ -1,10 +1,11 @@
 import requests
 from cStringIO import StringIO
 
+from django.conf import settings
 from django.core.files.uploadedfile import InMemoryUploadedFile
-from django.db import models
+from django.db import models, transaction
 
-from django_images.models import Image as BaseImage
+from django_images.models import Image as BaseImage, Thumbnail
 from taggit.managers import TaggableManager
 
 from ..users.models import User
@@ -19,7 +20,13 @@ class ImageManager(models.Manager):
         buf.write(response.content)
         obj = InMemoryUploadedFile(buf, 'image', file_name,
                                    None, buf.tell(), None)
-        return Image.objects.create(image=obj)
+        # create the image and its thumbnails in one transaction, removing
+        # a chance of getting Database into a inconsistent state when we
+        # try to create thumbnails one by one later
+        image = self.create(image=obj)
+        for size in settings.IMAGE_SIZES.keys():
+            Thumbnail.objects.get_or_create_at_size(image.pk, size)
+        return image
 
 
 class Image(BaseImage):

pinry/core/tests/helpers.py

@@ -3,6 +3,7 @@ from django.contrib.auth.models import Permission
 from django.core.files.images import ImageFile
 from django.db.models.query import QuerySet
 from django.test import TestCase
+from django_images.models import Thumbnail
 
 import factory
 from taggit.models import Tag
@@ -33,8 +34,15 @@ class TagFactory(factory.Factory):
 
 
 class ImageFactory(factory.Factory):
+    FACTORY_FOR = Image
+
     image = factory.LazyAttribute(lambda a: ImageFile(open(TEST_IMAGE_PATH, 'rb')))
 
+    @factory.post_generation()
+    def create_thumbnails(self, create, extracted, **kwargs):
+        for size in settings.IMAGE_SIZES.keys():
+            Thumbnail.objects.get_or_create_at_size(self.pk, size)
+
 
 class PinFactory(factory.Factory):
     submitter = factory.SubFactory(UserFactory)

pinry/core/views.py

@@ -1,9 +1,11 @@
 from django.http import HttpResponseRedirect
+from django.conf import settings
 from django.core.urlresolvers import reverse
 from django.views.generic import CreateView
 from django_images.models import Image
 
 from braces.views import JSONResponseMixin, LoginRequiredMixin
+from django_images.models import Thumbnail
 
 from .forms import ImageForm
 
@@ -20,6 +22,8 @@ class CreateImage(JSONResponseMixin, LoginRequiredMixin, CreateView):
 
     def form_valid(self, form):
         image = form.save()
+        for size in settings.IMAGE_SIZES.keys():
+            Thumbnail.objects.get_or_create_at_size(image.pk, size)
         return self.render_json_response({
             'success': {
                 'id': image.id