django-orm

The documentation for Django 1.7 mentions RunSQL classes can be used to create partial indexes on your tables. I have a table where I want the combination of title , blog & category to be unique. However if category is not provided, the combination of title & blog should still be unique. class Post(models.Model): title = models.CharField(max_length=200) blog = models.ForeignKey(Blog) category = models.ForeignKey(Category, null=True, blank=True) I can achieve this constraint with partial indexes (like the SQL shown below). Where do I add this code if I'm using Django 1.7 migrations? CREATE

I have the following models: class City(models.Model): ... class Census(models.Model): city = models.ForeignKey(City) date = models.DateTimeField() value = models.BigIntegerField() Now I'd like to annotate a City-queryset with the value of the latest Census. How do I achieve that? I have tried: City.objects.annotate(population=Max('census__date')) # --> annotates date and not value City.objects.annotate(population=Max('census__value')) # --> annotates highest value, not latest City.objects.annotate(population= Case( When( census__date=Max('census__date'), then='census__value') ) ) # -->

Short Question What is the default order of a list returned from a Django filter call when connected to a PostgreSQL database? Background By my own admission, I had made a poor assumption at the application layer in that the order in which a list is returned will be constant, that is without using 'order_by'. The list of items I was querying is not in alphabetic order or any other deliberate order. It was thought to remain in the same order as which they were added to the database. This assumption held true for hundreds of queries, but a failure was reported by my application when the order

Prologue: This is a question arising often in SO: Django Models Group By Django equivalent for count and group by How to query as GROUP BY in django? How to use the ORM for the equivalent of a SQL count, group and join query? I have composed an example on SO Documentation but since the Documentation will get shut down on August 8, 2017, I will follow the suggestion of this widely upvoted and discussed meta answer and transform my example to a self-answered post. Of course, I would be more than happy to see any different approach as well!! Question: Assume the model: class Books(models.Model):

This question already has an answer here: How to do many-to-many Django query to find book with 2 given authors? 4 answers I have a pk list of instances of Tag model, say pk_list = [10, 6, 3] I have another model with m2m field of tags and an instance that contains exactly 3 tags (of above pks). class Node(models.Model): ... tags = models.ManyToManyField(Tag, related_name='nodes') I'd like to retrieve a Node that contains exact set of tags as specified in my pk_list. When I do Node.objects.filter(tags__in=pk_list) it returns a list of three same instances [<Node: My node title>, <Node: My node

I have a custom manager. I want to use it for related objects. I found use_for_related_fields in docs. But it does not work the way I used it: class RandomQueryset(models.query.QuerySet): def randomize(self): count = self.count() random_index = random.randint(0, count - 1) return self.all()[random_index] class RandomManager(models.Manager): use_for_related_fields = True def get_query_set(self): return RandomQueryset(self.model, using=self._db) def randomize(self): return self.get_query_set().randomize() I used it for one model: >>> post = PostPages.default_manager.filter(image_gallery__isnull