I have the below structure, where content modules, which are subclassed from a common model, are attached to pages via a 'page module' model that references them via a GenericForeignKey:
class SitePage(models.Model):
title = models.CharField()
# [etc..]
class PageModule(models.Model):
page = models.ForeignKey(SitePage, db_index=True, on_delete=models.CASCADE)
module_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
module_id = models.PositiveIntegerField()
module_object = GenericForeignKey("module_type", "module_id")
class CommonModule(models.Model):
published_time = models.DateTimeField()
class SingleImage(CommonModule):
title = models.CharField()
# [etc..]
class Article(CommonModule):
title = models.CharField()
# [etc..]
At the moment, populating pages from this results in a LOT of SQL queries. I want to fetch all the module contents (i.e. all the SingleImage and Article instances) for a given page in the most database-efficient manner.
I can't just do a straight prefetch_related because it "must be restricted to a homogeneous set of results", and I'm fetching multiple content types.
I can get each module type individually:
image_modules = PageModule.objects.filter(page=whatever_page, module_type=ContentType.objects.get_for_model(SingleImage)).prefetch_related('module_object_')
article_modules = PageModule.objects.filter(page=whatever_page, module_type=ContentType.objects.get_for_model(Article)).prefetch_related('module_object')
all_modules = image_modules | article_modules
But I need to sort them:
all_modules.order_by('module_object__published_time')
and I can't because:
"Field 'module_object' does not generate an automatic reverse relation and therefore cannot be used for reverse querying"
... and I don't think I can add the recommended GenericRelation field to all the content models because there's already content in there.
So... can I do this at all? Or am I stuck?
