add implementation of IntFlag as ListField of IntEnumField

extras_mongoengine/fields.py

@@ -1,6 +1,14 @@
+import operator
+
 from datetime import timedelta
 from mongoengine.base import BaseField
-from mongoengine.fields import IntField, StringField, EmailField
+from mongoengine.fields import EmailField, IntField, ListField, StringField
+
+try:
+    from functools import reduce
+except ImportError:
+    # reduce is a builtin in Python2
+    pass
 
 
 class TimedeltaField(BaseField):
@@ -105,6 +113,33 @@ class IntEnumField(EnumField, IntField):
     pass
 
 
+class IntFlagField(ListField):
+    def __init__(self, enum, **kwargs):
+        super(IntFlagField, self).__init__(IntEnumField(enum), **kwargs)
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+
+        return self.field.enum(reduce(
+            operator.or_, instance._data.get(self.name, []), 0))
+
+    def __set__(self, instance, value):
+        # copy mongoengine
+        if value is None:
+            if self.null:
+                value = None
+            elif self.default is not None:
+                value = self.default
+                if callable(value):
+                    value = value()
+
+        if value is not None and not isinstance(value, list):
+            value = [i for i in self.field.enum if i and i & value == i]
+
+        super(IntFlagField, self).__set__(instance, value)
+
+
 class StringEnumField(EnumField, StringField):
     """A variation on :class:`EnumField` for only string containing enumeration.
     """