if alias is null set to first 5 lower characters of the name if alias is null set to first 5 lower characters of the name
from django.db.models import Value as V
from django.db.models.functions import Lower, StrIndex, Substr, Upper
from django.test import TestCase

from ..models import Author


class SubstrTests(TestCase):
    def test_basic(self):
        Author.objects.create(name="John Smith", alias="smithj")
        Author.objects.create(name="Rhonda")
        authors = Author.objects.annotate(name_part=Substr("name", 5, 3))
        self.assertQuerySetEqual(
            authors.order_by("name"), [" Sm", "da"], lambda a: a.name_part
        )
        authors = Author.objects.annotate(name_part=Substr("name", 2))
        self.assertQuerySetEqual(
            authors.order_by("name"), ["ohn Smith", "honda"], lambda a: a.name_part
        )
        
        Author.objects.filter(alias__isnull=True).update(
            alias=Lower(Substr("name", 1, 5)),
        )
        self.assertQuerySetEqual(
            authors.order_by("name"), ["smithj", "rhond"], lambda a: a.alias
        )

    def test_start(self):
        Author.objects.create(name="John Smith", alias="smithj")
        a = Author.objects.annotate(
            name_part_1=Substr("name", 1),
            name_part_2=Substr("name", 2),
        ).get(alias="smithj")

        self.assertEqual(a.name_part_1[1:], a.name_part_2)

    def test_pos_gt_zero(self):
        with self.assertRaisesMessage(ValueError, "'pos' must be greater than 0"):
            Author.objects.annotate(raises=Substr("name", 0))

    def test_expressions(self):
        Author.objects.create(name="John Smith", alias="smithj")
        Author.objects.create(name="Rhonda")
        substr = Substr(Upper("name"), StrIndex("name", V("h")), 5)
        authors = Author.objects.annotate(name_part=substr)
        self.assertQuerySetEqual(
            authors.order_by("name"), ["HN SM", "HONDA"], lambda a: a.name_part
        )