django/tests/db_functions/text/test_pad.py

from django.db import connection
from django.db.models import Value
from django.db.models.functions import Length, LPad, RPad
from django.test import TestCase

from ..models import Author


class PadTests(TestCase):
    def test_pad(self):
        Author.objects.create(name="John", alias="j")
        none_value = (
            "" if connection.features.interprets_empty_strings_as_nulls else None
        )
        tests = (
            (LPad("name", 7, Value("xy")), "xyxJohn"),
            (RPad("name", 7, Value("xy")), "Johnxyx"),
            (LPad("name", 6, Value("x")), "xxJohn"),
            (RPad("name", 6, Value("x")), "Johnxx"),
            # The default pad string is a space.
            (LPad("name", 6), "  John"),
            (RPad("name", 6), "John  "),
            # If string is longer than length it is truncated.
            (LPad("name", 2), "Jo"),
            (RPad("name", 2), "Jo"),
            (LPad("name", 0), ""),
            (RPad("name", 0), ""),
            (LPad("name", None), none_value),
            (RPad("name", None), none_value),
            (LPad(Value(None), 1), none_value),
            (RPad(Value(None), 1), none_value),
            (LPad("goes_by", 1), none_value),
            (RPad("goes_by", 1), none_value),
        )
        for function, padded_name in tests:
            with self.subTest(function=function):
                authors = Author.objects.annotate(padded_name=function)
                self.assertQuerySetEqual(
                    authors, [padded_name], lambda a: a.padded_name, ordered=False
                )

    def test_pad_negative_length(self):
        for function in (LPad, RPad):
            with self.subTest(function=function):
                with self.assertRaisesMessage(
                    ValueError, "'length' must be greater or equal to 0."
                ):
                    function("name", -1)

    def test_combined_with_length(self):
        Author.objects.create(name="Rhonda", alias="john_smith")
        Author.objects.create(name="♥♣♠", alias="bytes")
        authors = Author.objects.annotate(filled=LPad("name", Length("alias")))
        self.assertQuerySetEqual(
            authors.order_by("alias"),
            ["  ♥♣♠", "    Rhonda"],
            lambda a: a.filled,
        )