id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36906	Oracle guard for coalescing text & varchar doesn't fathom JSONField	Jacob Walls	kanin.kearpimy@…	"`Coalesce` has an `as_oracle()` method to make sure that `varchar` and `NCLOB` (text) fields are not mixed. `JSONField` is also implemented as an `NCLOB` type, so it needs to be included in the check, too.

Discovered in https://github.com/django/django/pull/20009#discussion_r2500562079.

Rough test for demonstration purposes -- a little more realism would be nice.

{{{#!diff
diff --git a/tests/db_functions/comparison/test_coalesce.py b/tests/db_functions/comparison/test_coalesce.py
index b08ae742df..839954f73c 100644
--- a/tests/db_functions/comparison/test_coalesce.py
+++ b/tests/db_functions/comparison/test_coalesce.py
@@ -1,4 +1,4 @@
-from django.db.models import Subquery, TextField
+from django.db.models import JSONField, Subquery, TextField
 from django.db.models.functions import Coalesce, Lower
 from django.test import TestCase
 from django.utils import timezone
@@ -51,6 +51,14 @@ class CoalesceTests(TestCase):
         self.assertQuerySetEqual(
             article.order_by(""title""), [lorem_ipsum.lower()], lambda a: a.headline
         )
+        # mixed JSON and Char
+        article = Article.objects.annotate(
+            # fix this to be more realistic?
+            summary_or_metadata=Coalesce(""summary"", ""metadata"", output_field=JSONField()),
+        )
+        self.assertQuerySetEqual(
+            article.order_by(""title""), [{}], lambda a: a.summary_or_metadata
+        )
 
     def test_ordering(self):
         Author.objects.create(name=""John Smith"", alias=""smithj"")
diff --git a/tests/db_functions/migrations/0002_create_test_models.py b/tests/db_functions/migrations/0002_create_test_models.py
index 2fa924cbe0..7c57a1eee7 100644
--- a/tests/db_functions/migrations/0002_create_test_models.py
+++ b/tests/db_functions/migrations/0002_create_test_models.py
@@ -50,6 +50,7 @@ class Migration(migrations.Migration):
                 (""published"", models.DateTimeField(null=True, blank=True)),
                 (""updated"", models.DateTimeField(null=True, blank=True)),
                 (""views"", models.PositiveIntegerField(default=0)),
+                (""metadata"", models.JSONField(default=dict)),
             ],
         ),
         migrations.CreateModel(
diff --git a/tests/db_functions/models.py b/tests/db_functions/models.py
index 45a5a027f4..7fb6200fb5 100644
--- a/tests/db_functions/models.py
+++ b/tests/db_functions/models.py
@@ -21,6 +21,7 @@ class Article(models.Model):
     published = models.DateTimeField(null=True, blank=True)
     updated = models.DateTimeField(null=True, blank=True)
     views = models.PositiveIntegerField(default=0)
+    metadata = models.JSONField(default=dict)
 
 
 class Fan(models.Model):
}}}

{{{#!py
django.db.utils.DatabaseError: ORA-00932: expression (""DB_FUNCTIONS_ARTICLE"".""METADATA"") is of data type NCLOB, which is incompatible with expected data type NCHAR
Help: https://docs.oracle.com/error-help/db/ora-00932/
}}}"	Bug	closed	Database layer (models, ORM)	dev	Normal	fixed			Ready for checkin	1	0	0	0	0	0