[Answered ]-Django Query (aggregates and counts)


Create a custom manager:

class ContainerManager(models.Manager):
    def get_query_set(self, *args, **kwargs):
        qs = super(ContainerManager, self).get_query_set(*args, **kwargs)
        annotations = {'tag_count':models.Count('tag'), 'com_count':models.Count('com')}
        return qs.annotate(**annotations)

class Container(models.Model):
    objects = ContainerManager()

Then, Container queries will always include tag_count and com_count attributes. You’ll probably need to modify the annotations, since I don’t have a copy of your model to refer to; I just guessed on the field names.


So after gaining a better understanding of your models, annotations won’t work for what you’re looking for. Really the only to get counts for how many Containers have kinds of ‘tag’ or ‘com’ is:

tag_count = Container.objects.filter(kind='tag').count()
com_count = Container.objects.filter(kind='com').count()

Annotations won’t give you that information. I think it’s possible to write your own aggregates and annotations, so that might be a possible solution. However, I’ve never done that myself, so I can’t really give you any guidance there. You’re probably stuck with using straight SQL.

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