from unittest import skipUnless

from django.db import connection

from django.db.models import Value

from django.db.models.functions import NullIf

from django.test import TestCase

from ..models import Author

class NullIfTests(TestCase):

    @classmethod

    def setUpTestData(cls):

        Author.objects.create(name="John Smith", alias="smithj")

        Author.objects.create(name="Rhonda", alias="Rhonda")

    def test_basic(self):

        authors = Author.objects.annotate(nullif=NullIf("alias", "name")).values_list(

            "nullif"

        )

        self.assertCountEqual(

            authors,

            [

                ("smithj",),

                (

                    ""

                    if connection.features.interprets_empty_strings_as_nulls

                    else None,

                ),

            ],

        )

    def test_null_argument(self):

        authors = Author.objects.annotate(

            nullif=NullIf("name", Value(None))

        ).values_list("nullif")

        self.assertCountEqual(authors, [("John Smith",), ("Rhonda",)])

    def test_too_few_args(self):

        msg = "'NullIf' takes exactly 2 arguments (1 given)"

        with self.assertRaisesMessage(TypeError, msg):

            NullIf("name")

    @skipUnless(connection.vendor == "oracle", "Oracle specific test for NULL-literal")

    def test_null_literal(self):

        msg = "Oracle does not allow Value(None) for expression1."

        with self.assertRaisesMessage(ValueError, msg):

            list(

                Author.objects.annotate(nullif=NullIf(Value(None), "name")).values_list(

                    "nullif"

                )

            )