Refs #33308 -- Deprecated support for passing encoded JSON string literals to JSONField & co.

JSON should be provided as literal Python objects an not in their
encoded string literal forms.

django/contrib/postgres/aggregates/general.py

@@ -1,8 +1,9 @@
+import json
 import warnings
 
 from django.contrib.postgres.fields import ArrayField
 from django.db.models import Aggregate, BooleanField, JSONField, TextField, Value
-from django.utils.deprecation import RemovedInDjango50Warning
+from django.utils.deprecation import RemovedInDjango50Warning, RemovedInDjango51Warning
 
 from .mixins import OrderableAggMixin
 
@@ -31,6 +32,14 @@ class DeprecatedConvertValueMixin:
             self._default_provided = True
         super().__init__(*expressions, default=default, **extra)
 
+    def resolve_expression(self, *args, **kwargs):
+        resolved = super().resolve_expression(*args, **kwargs)
+        if not self._default_provided:
+            resolved.empty_result_set_value = getattr(
+                self, "deprecation_empty_result_set_value", self.deprecation_value
+            )
+        return resolved
+
     def convert_value(self, value, expression, connection):
         if value is None and not self._default_provided:
             warnings.warn(self.deprecation_msg, category=RemovedInDjango50Warning)
@@ -48,8 +57,7 @@ class ArrayAgg(DeprecatedConvertValueMixin, OrderableAggMixin, Aggregate):
     deprecation_msg = (
         "In Django 5.0, ArrayAgg() will return None instead of an empty list "
         "if there are no rows. Pass default=None to opt into the new behavior "
-        "and silence this warning or default=Value([]) to keep the previous "
-        "behavior."
+        "and silence this warning or default=[] to keep the previous behavior."
     )
 
     @property
@@ -87,13 +95,46 @@ class JSONBAgg(DeprecatedConvertValueMixin, OrderableAggMixin, Aggregate):
 
     # RemovedInDjango50Warning
     deprecation_value = "[]"
+    deprecation_empty_result_set_value = property(lambda self: [])
     deprecation_msg = (
         "In Django 5.0, JSONBAgg() will return None instead of an empty list "
         "if there are no rows. Pass default=None to opt into the new behavior "
-        "and silence this warning or default=Value('[]') to keep the previous "
+        "and silence this warning or default=[] to keep the previous "
         "behavior."
     )
 
+    # RemovedInDjango51Warning: When the deprecation ends, remove __init__().
+    #
+    # RemovedInDjango50Warning: When the deprecation ends, replace with:
+    # def __init__(self, *expressions, default=None, **extra):
+    def __init__(self, *expressions, default=NOT_PROVIDED, **extra):
+        super().__init__(*expressions, default=default, **extra)
+        if (
+            isinstance(default, Value)
+            and isinstance(default.value, str)
+            and not isinstance(default.output_field, JSONField)
+        ):
+            value = default.value
+            try:
+                decoded = json.loads(value)
+            except json.JSONDecodeError:
+                warnings.warn(
+                    "Passing a Value() with an output_field that isn't a JSONField as "
+                    "JSONBAgg(default) is deprecated. Pass default="
+                    f"Value({value!r}, output_field=JSONField()) instead.",
+                    stacklevel=2,
+                    category=RemovedInDjango51Warning,
+                )
+                self.default.output_field = self.output_field
+            else:
+                self.default = Value(decoded, self.output_field)
+                warnings.warn(
+                    "Passing an encoded JSON string as JSONBAgg(default) is "
+                    f"deprecated. Pass default={decoded!r} instead.",
+                    stacklevel=2,
+                    category=RemovedInDjango51Warning,
+                )
+
 
 class StringAgg(DeprecatedConvertValueMixin, OrderableAggMixin, Aggregate):
     function = "STRING_AGG"
@@ -106,8 +147,7 @@ class StringAgg(DeprecatedConvertValueMixin, OrderableAggMixin, Aggregate):
     deprecation_msg = (
         "In Django 5.0, StringAgg() will return None instead of an empty "
         "string if there are no rows. Pass default=None to opt into the new "
-        "behavior and silence this warning or default=Value('') to keep the "
-        "previous behavior."
+        'behavior and silence this warning or default="" to keep the previous behavior.'
     )
 
     def __init__(self, expression, delimiter, **extra):

django/db/models/aggregates.py

@@ -85,6 +85,8 @@ class Aggregate(Func):
             return c
         if hasattr(default, "resolve_expression"):
             default = default.resolve_expression(query, allow_joins, reuse, summarize)
+            if default._output_field_or_none is None:
+                default.output_field = c._output_field_or_none
         else:
             default = Value(default, c._output_field_or_none)
         c.default = None  # Reset the default argument before wrapping.

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
         )

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)
 

django/db/models/sql/compiler.py

@@ -1637,9 +1637,7 @@ class SQLInsertCompiler(SQLCompiler):
                     "Window expressions are not allowed in this query (%s=%r)."
                     % (field.name, value)
                 )
-        else:
-            value = field.get_db_prep_save(value, connection=self.connection)
-        return value
+        return field.get_db_prep_save(value, connection=self.connection)
 
     def pre_save_val(self, field, obj):
         """
@@ -1893,18 +1891,14 @@ class SQLUpdateCompiler(SQLCompiler):
                     )
             elif hasattr(val, "prepare_database_save"):
                 if field.remote_field:
-                    val = field.get_db_prep_save(
-                        val.prepare_database_save(field),
-                        connection=self.connection,
-                    )
+                    val = val.prepare_database_save(field)
                 else:
                     raise TypeError(
                         "Tried to update field %s with a model instance, %r. "
                         "Use a value compatible with %s."
                         % (field, val, field.__class__.__name__)
                     )
-            else:
-                val = field.get_db_prep_save(val, connection=self.connection)
+            val = field.get_db_prep_save(val, connection=self.connection)
 
             # Getting the placeholder for the field.
             if hasattr(field, "get_placeholder"):

django/db/models/sql/query.py

@@ -522,9 +522,9 @@ class Query(BaseExpression):
         result = compiler.execute_sql(SINGLE)
         if result is None:
             result = empty_set_result
-
-        converters = compiler.get_converters(outer_query.annotation_select.values())
-        result = next(compiler.apply_converters((result,), converters))
+        else:
+            converters = compiler.get_converters(outer_query.annotation_select.values())
+            result = next(compiler.apply_converters((result,), converters))
 
         return dict(zip(outer_query.annotation_select, result))