2 files changed, 33 insertions, 2 deletions
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 2a98396cad..cd995de80f 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -921,6 +921,8 @@ class Field(RegisterLookupMixin):
 
     def get_db_prep_save(self, value, connection):
         """Return field's value prepared for saving into a database."""
+        if hasattr(value, "as_sql"):
+            return value
         return self.get_db_prep_value(value, connection=connection, prepared=False)
 
     def has_default(self):
@@ -1715,6 +1717,8 @@ class DecimalField(Field):
     def get_db_prep_value(self, value, connection, prepared=False):
         if not prepared:
             value = self.get_prep_value(value)
+        if hasattr(value, "as_sql"):
+            return value
         return connection.ops.adapt_decimalfield_value(
             value, self.max_digits, self.decimal_places
         )
diff --git a/django/db/models/fields/json.py b/django/db/models/fields/json.py
index c0242bd7be..eb2d35f100 100644
--- a/django/db/models/fields/json.py
+++ b/django/db/models/fields/json.py
@@ -1,9 +1,10 @@
 import json
+import warnings
 
 from django import forms
 from django.core import checks, exceptions
 from django.db import NotSupportedError, connections, router
-from django.db.models import lookups
+from django.db.models import expressions, lookups
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.fields import TextField
 from django.db.models.lookups import (
@@ -11,6 +12,7 @@ from django.db.models.lookups import (
     PostgresOperatorLookup,
     Transform,
 )
+from django.utils.deprecation import RemovedInDjango51Warning
 from django.utils.translation import gettext_lazy as _
 
 from . import Field
@@ -97,7 +99,32 @@ class JSONField(CheckFieldDefaultMixin, Field):
         return "JSONField"
 
     def get_db_prep_value(self, value, connection, prepared=False):
-        if hasattr(value, "as_sql"):
+        # RemovedInDjango51Warning: When the deprecation ends, replace with:
+        # if (
+        #     isinstance(value, expressions.Value)
+        #     and isinstance(value.output_field, JSONField)
+        # ):
+        #     value = value.value
+        # elif hasattr(value, "as_sql"): ...
+        if isinstance(value, expressions.Value):
+            if isinstance(value.value, str) and not isinstance(
+                value.output_field, JSONField
+            ):
+                try:
+                    value = json.loads(value.value, cls=self.decoder)
+                except json.JSONDecodeError:
+                    value = value.value
+                else:
+                    warnings.warn(
+                        "Providing an encoded JSON string via Value() is deprecated. "
+                        f"Use Value({value!r}, output_field=JSONField()) instead.",
+                        category=RemovedInDjango51Warning,
+                    )
+            elif isinstance(value.output_field, JSONField):
+                value = value.value
+            else:
+                return value
+        elif hasattr(value, "as_sql"):
             return value
         return connection.ops.adapt_json_value(value, self.encoder)