use create_decimal128_context

Author: jschlyter

mongoengine/fields.py

@@ -12,7 +12,7 @@
 import gridfs
 import pymongo
 from bson import SON, Binary, DBRef, ObjectId
-from bson.decimal128 import Decimal128
+from bson.decimal128 import Decimal128, create_decimal128_context
 from bson.int64 import Int64
 from pymongo import ReturnDocument
 
@@ -2642,6 +2642,9 @@ def to_mongo(self, document):
 
 
 class Decimal128Field(BaseField):
+
+    DECIMAL_CONTEXT = create_decimal128_context()
+
     def __init__(self, min_value=None, max_value=None, **kwargs):
         self.min_value = min_value
         self.max_value = max_value
@@ -2659,8 +2662,9 @@ def to_mongo(self, value):
             return None
         if isinstance(value, Decimal128):
             return value
-        if isinstance(value, (int, float)):
-            return Decimal128(str(value))
+        if not isinstance(value, decimal.Decimal):
+            with decimal.localcontext(self.DECIMAL_CONTEXT) as ctx:
+                value = ctx.create_decimal(value)
         return Decimal128(value)
 
     def to_python(self, value):

tests/fields/test_decimal128_field.py

@@ -105,7 +105,7 @@ def test_storage(self):
         model = Decimal128Document(dec128_fld=100.0).save()
         assert get_as_pymongo(model) == {
             "_id": model.id,
-            "dec128_fld": Decimal128("100.0"),
+            "dec128_fld": Decimal128("100"),
         }
 
         # from Decimal
@@ -124,7 +124,7 @@ def test_storage(self):
 
     def test_json(self):
         Decimal128Document.drop_collection()
-        f = random.random()
+        f = str(random.random())
         Decimal128Document(dec128_fld=f).save()
         json_str = Decimal128Document.objects.to_json()
         array = json.loads(json_str)