fix DatabaseOperations.convert_decimalfield_value() crash on ints

Author: timgraham

django_mongodb/features.py

@@ -76,10 +76,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "model_fields.test_jsonfield.TestQuerying.test_order_grouping_custom_decoder",
         "model_fields.test_jsonfield.TestQuerying.test_ordering_by_transform",
         "model_fields.test_jsonfield.TestQuerying.test_ordering_grouping_by_key_transform",
-        # DatabaseOperations.convert_decimalfield_value() crash:
-        # 'int' object has no attribute 'to_decimal'.
-        "expressions.tests.ExpressionsNumericTests.test_filter_decimal_expression",
-        "expressions.tests.ValueTests.test_output_field_decimalfield",
         # pymongo.errors.OperationFailure:  $multiply only supports numeric
         # types, not date. (should be wrapped in DatabaseError).
         "expressions.tests.FTimeDeltaTests.test_invalid_operator",

django_mongodb/operations.py

@@ -2,6 +2,7 @@
 import json
 import re
 import uuid
+from decimal import Decimal
 
 from bson.decimal128 import Decimal128
 from django.conf import settings
@@ -98,7 +99,12 @@ def convert_datetimefield_value(self, value, expression, connection):
     def convert_decimalfield_value(self, value, expression, connection):
         if value is not None:
             # from Decimal128 to decimal.Decimal()
-            value = value.to_decimal()
+            try:
+                value = value.to_decimal()
+            except AttributeError:
+                # `value` could be an integer in the case of an annotation
+                # like ExpressionWrapper(Value(1), output_field=DecimalField().
+                return Decimal(value)
         return value
 
     def convert_durationfield_value(self, value, expression, connection):