Merge pull request #45 from jetavator/issue-43-Return_type_of_UserPro…

…perty_defaults_should_always_be_property_type

Add persist_defaults param to UserProperty

features/dict.feature

@@ -227,4 +227,7 @@ Feature: Test dictionary DOM objects
       """
       example.current_address.first_line == "123 Fake Street"
       example.previous_addresses[0].first_line == "123 Fake Street"
+      type(example.vehicles) is wysdom.dom.DOMDict
+      document(example.vehicles) is example
+      example.vehicles is example.vehicles
       """

features/examples/modules/dict_module.py

@@ -26,4 +26,4 @@ class Person(UserObject):
         Address,
         default_function=lambda person: person.previous_addresses[0])
     previous_addresses: List[Address] = UserProperty(SchemaArray(Address))
-    vehicles: Dict[str, Vehicle] = UserProperty(SchemaDict(Vehicle), default={})
+    vehicles: Dict[str, Vehicle] = UserProperty(SchemaDict(Vehicle), default={}, persist_defaults=True)

features/steps/steps.py

@@ -1,5 +1,6 @@
 from behave import *
 
+import wysdom
 from wysdom import document, parent, key, schema
 
 import os

wysdom/__version__.py

@@ -1,3 +1,3 @@
-VERSION = (0, 1, 4)
+VERSION = (0, 1, 5)
 
 __version__ = '.'.join(map(str, VERSION))

wysdom/user_objects/UserProperty.py

@@ -2,7 +2,7 @@
 
 from ..base_schema import Schema
 from ..object_schema import resolve_arg_to_schema
-from ..dom import DOMObject
+from ..dom import DOMObject, DOMInfo, document
 
 
 class UserProperty(object):
@@ -38,6 +38,13 @@ class UserProperty(object):
                              passed the :class:`~.wysdom.user_objects.UserObject` instance that
                              owns the property. Cannot be set in conjunction
                              with `default`.
+
+    :param persist_defaults: If this property is set to True and a UserProperty has either the
+                             `default` or `default_function` property, when the UserProperty returns
+                             a default value that value will also be explicitly stored in the underlying
+                             data object. This is often desirable behavior if the UserProperty
+                             returns another object and your code expects it to return the same
+                             object instance each time it is accessed.
     """
 
     def __init__(
@@ -46,7 +53,8 @@ def __init__(
             optional: Optional[bool] = None,
             name: Optional[str] = None,
             default: Optional[Any] = None,
-            default_function: Optional[Callable] = None
+            default_function: Optional[Callable] = None,
+            persist_defaults: Optional[bool] = None
     ) -> None:
         if default is not None or default_function is not None:
             if default is not None and default_function is not None:
@@ -61,6 +69,7 @@ def __init__(
         self.name = name
         self.default = default
         self.default_function = default_function
+        self.persist_defaults = persist_defaults
 
     def __get__(
             self,
@@ -72,9 +81,23 @@ def __get__(
                 "UserProperty is not valid as a class data descriptor")
         if self.name not in instance:
             if self.default_function:
-                return self.default_function(instance)
+                default_value = self.default_function(instance)
+            else:
+                default_value = self.default
+            if self.persist_defaults:
+                instance[self.name] = default_value
+                return instance[self.name]
+            elif default_value is None:
+                return default_value
             else:
-                return self.default
+                return self.schema_type(
+                    default_value,
+                    DOMInfo(
+                        document=document(instance),
+                        parent=instance,
+                        element_key=self.name
+                    )
+                )
         return instance[self.name]
 
     def __set__(