[FIXED] How to override queryset count() method in Django's admin list

Issue

In order to avoid time consuming and costly exact database count queries, I'd like to override the count() method inside a Django admin class like so:

from django.contrib import admin
from django.db import connection

class CountProxy:
    def __call__(self):
        # how to access the queryset `query` here?
        query = ...

        try:
            if not query.where:
                cursor = connection.cursor()
                cursor.execute("SELECT reltuples FROM pg_class WHERE relname = %s", [query.model._meta.db_table])
                n = int(cursor.fetchone()[0])
                if n >= 1000: return n # exact count for small tables
            return object_list.count()
        except:
            # exception for lists
            return len(object_list)
        return estimated_count

class MyAdmin(admin.ModelAdmin):
    def get_queryset(self, request):
        qs = super(MyAdmin, self).get_queryset(request)
        qs.count = CountProxy()
        return qs

But I don#t know how to access the original queryset within my CountProxy class. Any idea? I know I can overwrite the whole changelist view through get_changelist. But that involves a lot of duplicating code from Django's repo.

Solution

I could be wrong, but could you pass qs as an instance attribute for CountProxy?

class CountProxy:
    def __init__(self, query):
        self.query = query

    def __call__(self):
        # you've already had the query here, do something with self.query

class MyAdmin(admin.ModelAdmin):
    def get_queryset(self, request):
        qs = super(MyAdmin, self).get_queryset(request)
        qs.count = CountProxy(qs)
        return qs

Answered By - Shang Wang

Answer Checked By - David Goodson (PHPFixing Volunteer)