Solve Pagination Issues: Avoid Inconsistent Results with Unordered Object Lists in Django

When working with pagination in Django, it is common to face issues related to inconsistent results, especially when paginating unordered object lists. These inconsistencies can confuse users, make data appear out of sequence, and potentially affect the user experience of your application. In this post, we’ll explain why these issues occur, how to identify them, and the best practices to resolve them.

Pagination is a powerful feature that allows data to be presented in chunks, making it easier for users to navigate large datasets. However, if the object list is unordered, pagination may not behave as expected, resulting in duplicate or missing items between pages. Let’s look at how to solve this problem effectively.

Why Pagination on Unordered Object Lists Can Be Problematic

Django’s ORM is designed to work efficiently with databases, but if you attempt to paginate an unordered queryset, you may run into issues. Unordered queries imply that there is no specific sequence in which the database returns records. When paginating such a queryset, it’s possible that the same item might appear on different pages, or that items might be skipped entirely.

This problem typically occurs because of how databases handle data retrieval. When there is no explicit ordering, the database engine decides the order arbitrarily, and this order can change between requests. Consequently, the items on page 1 might change when you request page 2, resulting in an inconsistent and confusing user experience.

How to Ensure Consistent Pagination

To ensure that pagination works consistently, it is crucial to add an explicit ordering to the queryset. This allows the database to return records in a predictable order, ensuring that pagination produces the correct and expected results each time.

Step 1: Add Ordering to Your Queryset

If you are using Django’s Generic ListView or manually paginating a queryset, add the order_by() clause to your queryset to define the order explicitly. For example:

from django.views.generic import ListView
from .models import MyModel

class MyModelListView(ListView):
    model = MyModel
    template_name = 'myapp/mymodel_list.html'
    context_object_name = 'objects'

    def get_queryset(self):
        return MyModel.objects.all().order_by('id')

from django.core.paginator import Paginator
from django.http import HttpRequest, JsonResponse
from .models import MyModel

def paginated_view(request: HttpRequest):
    objects = MyModel.objects.all().order_by('created_at')
    paginator = Paginator(objects, 10)  # Show 10 objects per page

    page_number = request.GET.get('page')
    page_obj = paginator.get_page(page_number)

    return JsonResponse({'data': list(page_obj.object_list.values()), 'has_next': page_obj.has_next()})

.order_by('created_at', 'id')