function.py

def randomly_order_queryset_deterministically(queryset, salt):
    """
    Applies a pseudo-random ordering on the queryset. For each object, a number
    is generated by performing a CRC32 function on the object's ID and a salt.
    So if you use the same salt, you get the same ordering.

    We need to implement it this way so the same random ordering is preserved for
    the subsequent AJAX requests.
    """
    return queryset.extra(
        select={
            'random_order': 'contactsindex_crc32(id ::text || %s)'
        },
        select_params=(salt, ),
        order_by=('random_order', 'id')
    )

migration.py

# -*- coding: utf-8 -*-
# Generated by Django 1.9.10 on 2016-12-20 12:48
from __future__ import unicode_literals

from django.db import migrations


CREATE_CRC32 = """
CREATE OR REPLACE FUNCTION contactsindex_crc32(text_string text) RETURNS bigint AS $$
DECLARE
    tmp bigint;
    i int;
    j int;
    byte_length int;
    binary_string bytea;
BEGIN
    IF text_string = '' THEN
        RETURN 0;
    END IF;

    i = 0;
    tmp = 4294967295;
    byte_length = bit_length(text_string) / 8;
    binary_string = decode(replace(text_string, E'\\\\', E'\\\\\\\\'), 'escape');
    LOOP
        tmp = (tmp # get_byte(binary_string, i))::bigint;
        i = i + 1;
        j = 0;
        LOOP
            tmp = ((tmp >> 1) # (3988292384 * (tmp & 1)))::bigint;
            j = j + 1;
            IF j >= 8 THEN
                EXIT;
            END IF;
        END LOOP;
        IF i >= byte_length THEN
            EXIT;
        END IF;
    END LOOP;
    RETURN (tmp # 4294967295);
END
$$ IMMUTABLE LANGUAGE plpgsql;
"""

DROP_CRC32 = "DROP FUNCTION contactsindex_crc32(text);"


class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0001_initial'),
    ]

    operations = [
        migrations.RunSQL(CREATE_CRC32, DROP_CRC32)
    ]