Serialize UnicodeSetAttributes correctly (#151)

Author: jmphilli

pynamodb/attributes.py

@@ -144,6 +144,48 @@ class UnicodeSetAttribute(SetMixin, Attribute):
     attr_type = STRING_SET
     null = True
 
+    def element_serialize(self, value):
+        """
+        This serializes unicode / strings out as unicode strings.
+        It does not touch the value if it is already a unicode str
+        :param value:
+        :return:
+        """
+        if isinstance(value, six.text_type):
+            return value
+        return six.u(str(value))
+
+    def element_deserialize(self, value):
+        """
+        This deserializes what we get from mongo back into a str
+        Serialization previously json encoded strings. This caused them to have
+        extra double quote (") characters. That no longer happens.
+        This method allows both types of serialized values to be read
+        :param value:
+        :return:
+        """
+        result = value
+        try:
+            result = json.loads(value)
+        except ValueError:
+            # it's serialized in the new way so pass
+            pass
+        return result
+
+    def serialize(self, value):
+        if value is not None:
+            try:
+                iter(value)
+            except TypeError:
+                value = [value]
+            if len(value):
+                return [self.element_serialize(val) for val in sorted(value)]
+        return None
+
+    def deserialize(self, value):
+        if value and len(value):
+            return set([self.element_deserialize(val) for val in value])
+
 
 class UnicodeAttribute(Attribute):
     """

pynamodb/tests/test_attributes.py

@@ -335,7 +335,8 @@ def test_unicode_set_serialize(self):
         self.assertEqual(attr.deserialize(None), None)
         self.assertEqual(
             attr.serialize(set([six.u('foo'), six.u('bar')])),
-            [json.dumps(val) for val in sorted(set([six.u('foo'), six.u('bar')]))])
+            sorted([six.u('foo'), six.u('bar')])
+        )
 
     def test_round_trip_unicode_set(self):
         """
@@ -353,9 +354,22 @@ def test_unicode_set_deserialize(self):
         UnicodeSetAttribute.deserialize
         """
         attr = UnicodeSetAttribute()
+        value = set([six.u('foo'), six.u('bar')])
+        self.assertEqual(
+            attr.deserialize(value),
+            value
+        )
+
+    def test_unicode_set_deserialize(self):
+        """
+        UnicodeSetAttribute.deserialize old way
+        """
+        attr = UnicodeSetAttribute()
+        value = set([six.u('foo'), six.u('bar')])
+        old_value = set([json.dumps(val) for val in value])
         self.assertEqual(
-            attr.deserialize([json.dumps(val) for val in sorted(set([six.u('foo'), six.u('bar')]))]),
-            set([six.u('foo'), six.u('bar')])
+            attr.deserialize(old_value),
+            value
         )
 
     def test_unicode_set_attribute(self):