I can't access QuerySet in Manager's init method in Django

Question

I'd like to get a QuerySet of a Model in Manager's __init__ method to setup Pagination for the QuerySet results. The reason why I want to setup Pagination in __init__ method is because I have lots of simple methods in the Manager like getPage and getNumberOfPages etc. to simplify abstraction and I don't want to duplicate the code to setup Paginator across all these methods.

For example, let's say that there is an Article model, which has a custom ArticleManager and it looks somewhat like this:

class ArticleManager(models.Manager):
    def __init__(self):
        super(ArticleManager, self).__init__()
        allObjects = super(ArticleManager, self).get_queryset()
        self.articlePaginator = Paginator(allObjects, 10)


class Article(models.Model):
    # blah blah
    # Model fields everywhere
    objects = ArticleManager()

Fourth line of this code that is super(ArticleManager, self).get_queryset() returns an AttributeError exception:

AttributeError: 'NoneType' object has no attribute '_meta'

I guess I should have done something more to properly initialize the Manager, but I'm not sure what it is. I've not found anything alike I want in Django docs or in other StackOverflow questions. Also I guess there might be something wrong in my approach, so if that's the case I'd be grateful if somebody would point that out.

Answer 1

You're calling the parent's get_query() method. You're not overriding it so there's no point, just call it on self . Better yet, make this operation lazy. Properties are an option:

class ArticleManager(models.Manager):
    @property
    def article_paginator(self):
        return Paginator(self.get_queryset(), 10)

Then you can access it via Article.objects.article_paginator .