DecimalField now stores as float not string (#289)

mongoengine/fields.py

@@ -260,30 +260,57 @@ class FloatField(BaseField):
 class DecimalField(BaseField):
     """A fixed-point decimal number field.
 
+    .. versionchanged:: 0.8
     .. versionadded:: 0.3
     """
 
-    def __init__(self, min_value=None, max_value=None, **kwargs):
-        self.min_value, self.max_value = min_value, max_value
+    def __init__(self, min_value=None, max_value=None, force_string=False,
+                 precision=2, rounding=decimal.ROUND_HALF_UP, **kwargs):
+        """
+        :param min_value: Validation rule for the minimum acceptable value.
+        :param max_value: Validation rule for the maximum acceptable value.
+        :param force_string: Store as a string.
+        :param precision: Number of decimal places to store.
+        :param rounding: The rounding rule from the python decimal libary:
+
+            - decimial.ROUND_CEILING (towards Infinity)
+            - decimial.ROUND_DOWN (towards zero)
+            - decimial.ROUND_FLOOR (towards -Infinity)
+            - decimial.ROUND_HALF_DOWN (to nearest with ties going towards zero)
+            - decimial.ROUND_HALF_EVEN (to nearest with ties going to nearest even integer)
+            - decimial.ROUND_HALF_UP (to nearest with ties going away from zero)
+            - decimial.ROUND_UP (away from zero)
+            - decimial.ROUND_05UP (away from zero if last digit after rounding towards zero would have been 0 or 5; otherwise towards zero)
+
+            Defaults to: ``decimal.ROUND_HALF_UP``
+
+        """
+        self.min_value = min_value
+        self.max_value = max_value
+        self.force_string = force_string
+        self.precision = decimal.Decimal(".%s" % ("0" * precision))
+        self.rounding = rounding
+
         super(DecimalField, self).__init__(**kwargs)
 
     def to_python(self, value):
-        original_value = value
-        if not isinstance(value, basestring):
-            value = unicode(value)
-        try:
-            value = decimal.Decimal(value)
-        except ValueError:
-            return original_value
-        return value
+        if value is None:
+            return value
+
+        return decimal.Decimal(value).quantize(self.precision,
+                                               rounding=self.rounding)
 
     def to_mongo(self, value):
-        return unicode(value)
+        if value is None:
+            return value
+        if self.force_string:
+            return unicode(value)
+        return float(self.to_python(value))
 
     def validate(self, value):
         if not isinstance(value, decimal.Decimal):
             if not isinstance(value, basestring):
-                value = str(value)
+                value = unicode(value)
             try:
                 value = decimal.Decimal(value)
             except Exception, exc:
@@ -295,6 +322,9 @@ class DecimalField(BaseField):
         if self.max_value is not None and value > self.max_value:
             self.error('Decimal value is too large')
 
+    def prepare_query_value(self, op, value):
+        return self.to_mongo(value)
+
 
 class BooleanField(BaseField):
     """A boolean field type.

mongoengine/queryset/transform.py

@@ -9,7 +9,7 @@ __all__ = ('query', 'update')
 
 
 COMPARISON_OPERATORS = ('ne', 'gt', 'gte', 'lt', 'lte', 'in', 'nin', 'mod',
-                          'all', 'size', 'exists', 'not')
+                        'all', 'size', 'exists', 'not')
 GEO_OPERATORS        = ('within_distance', 'within_spherical_distance',
                         'within_box', 'within_polygon', 'near', 'near_sphere',
                         'max_distance')
@@ -74,7 +74,7 @@ def query(_doc_cls=None, _field_operation=False, **query):
             if op in singular_ops:
                 if isinstance(field, basestring):
                     if (op in STRING_OPERATORS and
-                        isinstance(value, basestring)):
+                       isinstance(value, basestring)):
                         StringField = _import_class('StringField')
                         value = StringField.prepare_query_value(op, value)
                     else:
@@ -144,7 +144,7 @@ def query(_doc_cls=None, _field_operation=False, **query):
         merge_query[k].append(mongo_query[k])
         del mongo_query[k]
         if isinstance(v, list):
-            value = [{k:val} for val in v]
+            value = [{k: val} for val in v]
             if '$and' in mongo_query.keys():
                 mongo_query['$and'].append(value)
             else: