Fix GenericReferenceField choices with DBRef and let it possible to set Document choice as string

mongoengine/base/fields.py

@@ -165,26 +165,29 @@ class BaseField(object):
         """
         pass
 
-    def _validate(self, value, **kwargs):
+    def _validate_choices(self, value):
         Document = _import_class('Document')
         EmbeddedDocument = _import_class('EmbeddedDocument')
 
+        choice_list = self.choices
+        if isinstance(choice_list[0], (list, tuple)):
+            choice_list = [k for k, v in choice_list]
+
+        # Choices which are other types of Documents
+        if isinstance(value, (Document, EmbeddedDocument)):
+            if not any(isinstance(value, c) for c in choice_list):
+                self.error(
+                    'Value must be instance of %s' % unicode(choice_list)
+                )
+        # Choices which are types other than Documents
+        elif value not in choice_list:
+            self.error('Value must be one of %s' % unicode(choice_list))
+
+
+    def _validate(self, value, **kwargs):
         # Check the Choices Constraint
         if self.choices:
-
-            choice_list = self.choices
-            if isinstance(self.choices[0], (list, tuple)):
-                choice_list = [k for k, v in self.choices]
-
-            # Choices which are other types of Documents
-            if isinstance(value, (Document, EmbeddedDocument)):
-                if not any(isinstance(value, c) for c in choice_list):
-                    self.error(
-                        'Value must be instance of %s' % unicode(choice_list)
-                    )
-            # Choices which are types other than Documents
-            elif value not in choice_list:
-                self.error('Value must be one of %s' % unicode(choice_list))
+            self._validate_choices(value)
 
         # check validation argument
         if self.validation is not None:

mongoengine/fields.py

@@ -1140,6 +1140,35 @@ class GenericReferenceField(BaseField):
     .. versionadded:: 0.3
     """
 
+    def __init__(self, *args, **kwargs):
+        choices = kwargs.pop('choices', None)
+        super(GenericReferenceField, self).__init__(*args, **kwargs)
+        self._original_choices = choices or []
+        self._cooked_choices = None
+
+    def _validate_choices(self, value):
+        if isinstance(value, dict):
+            # If the field has not been dereferenced, it is still a dict
+            # of class and DBRef
+            if value.get('_cls') in [c.__name__ for c in self.choices]:
+                return
+        super(GenericReferenceField, self)._validate_choices(value)
+
+    @property
+    def choices(self):
+        if self._cooked_choices is None:
+            self._cooked_choices = []
+            for choice in self._original_choices:
+                if isinstance(choice, basestring):
+                    choice = get_document(choice)
+                self._cooked_choices.append(choice)
+        return self._cooked_choices
+
+    @choices.setter
+    def choices(self, value):
+        self._original_choices = value
+        self._cooked_choices = None
+
     def __get__(self, instance, owner):
         if instance is None:
             return self