[4.2.x] Fixed #34544 -- Avoided DBMS_LOB.SUBSTR() wrapping with IS NULL condition on Oracle.

Regression in 09ffc5c1212d4ced58b708cbbf3dfbfb77b782ca.

Thanks Michael Smith for the report.

This also reverts commit 1e4da439556cdd69eb9f91e07f99cf77997e70d2.
Backport of 1586a09b7949bbb7b0d84cb74ce1cadc25cbb355 from main

django/db/backends/oracle/operations.py

@@ -296,12 +296,6 @@ END;
             columns.append(value[0])
         return tuple(columns)
 
-    def field_cast_sql(self, db_type, internal_type):
-        if db_type and db_type.endswith("LOB") and internal_type != "JSONField":
-            return "DBMS_LOB.SUBSTR(%s)"
-        else:
-            return "%s"
-
     def no_limit_value(self):
         return None
 
@@ -344,7 +338,9 @@ END;
     def lookup_cast(self, lookup_type, internal_type=None):
         if lookup_type in ("iexact", "icontains", "istartswith", "iendswith"):
             return "UPPER(%s)"
-        if internal_type == "JSONField" and lookup_type == "exact":
+        if (
+            lookup_type != "isnull" and internal_type in ("BinaryField", "TextField")
+        ) or (lookup_type == "exact" and internal_type == "JSONField"):
             return "DBMS_LOB.SUBSTR(%s)"
         return "%s"
 

django/db/backends/postgresql/features.py

@@ -82,6 +82,9 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "indexes.tests.SchemaIndexesNotPostgreSQLTests."
             "test_create_index_ignores_opclasses",
         },
+        "PostgreSQL requires casting to text.": {
+            "lookup.tests.LookupTests.test_textfield_exact_null",
+        },
     }
 
     @cached_property

docs/releases/4.2.2.txt

@@ -9,4 +9,6 @@ Django 4.2.2 fixes several bugs in 4.2.1.
 Bugfixes
 ========
 
-* ...
+* Fixed a regression in Django 4.2 that caused an unnecessary
+  ``DBMS_LOB.SUBSTR()`` wrapping in the ``__isnull`` and ``__exact=None``
+  lookups for ``TextField()``/``BinaryField()`` on Oracle (:ticket:`34544`).

tests/lookup/models.py

@@ -19,6 +19,7 @@ class Alarm(models.Model):
 class Author(models.Model):
     name = models.CharField(max_length=100)
     alias = models.CharField(max_length=50, null=True, blank=True)
+    bio = models.TextField(null=True)
 
     class Meta:
         ordering = ("name",)
@@ -50,22 +51,11 @@ class NulledTextField(models.TextField):
         return None if value == "" else value
 
 
-class NullField(models.Field):
-    pass
-
-
-NullField.register_lookup(IsNull)
-
-
 @NulledTextField.register_lookup
 class NulledTransform(models.Transform):
     lookup_name = "nulled"
     template = "NULL"
 
-    @property
-    def output_field(self):
-        return NullField()
-
 
 @NulledTextField.register_lookup
 class IsNullWithNoneAsRHS(IsNull):

tests/lookup/tests.py

@@ -49,7 +49,7 @@ class LookupTests(TestCase):
     @classmethod
     def setUpTestData(cls):
         # Create a few Authors.
-        cls.au1 = Author.objects.create(name="Author 1", alias="a1")
+        cls.au1 = Author.objects.create(name="Author 1", alias="a1", bio="x" * 4001)
         cls.au2 = Author.objects.create(name="Author 2", alias="a2")
         # Create a few Articles.
         cls.a1 = Article.objects.create(
@@ -1000,6 +1000,13 @@ class LookupTests(TestCase):
         Season.objects.create(year=2012, gt=None)
         self.assertQuerySetEqual(Season.objects.filter(gt__regex=r"^$"), [])
 
+    def test_textfield_exact_null(self):
+        with self.assertNumQueries(1) as ctx:
+            self.assertSequenceEqual(Author.objects.filter(bio=None), [self.au2])
+        # Columns with IS NULL condition are not wrapped (except PostgreSQL).
+        bio_column = connection.ops.quote_name(Author._meta.get_field("bio").column)
+        self.assertIn(f"{bio_column} IS NULL", ctx.captured_queries[0]["sql"])
+
     def test_regex_non_string(self):
         """
         A regex lookup does not fail on non-string fields