diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -104,15 +104,22 @@
     SWH loader."""
     origin = attr.ib(type=Origin)
     date = attr.ib(type=datetime.datetime)
+    status = attr.ib(
+        type=str,
+        validator=attr.validators.in_(['ongoing', 'full', 'partial']))
+    type = attr.ib(type=str)
+    snapshot = attr.ib(type=Sha1Git)
+    metadata = attr.ib(type=Optional[Dict[str, object]],
+                       default=None)
+
     visit = attr.ib(type=Optional[int],
-                    validator=attr.validators.optional([]))
+                    default=None)
     """Should not be set before calling 'origin_visit_add()'."""
 
     def to_dict(self):
         """Serializes the date as a string and omits the visit id if it is
         `None`."""
         ov = super().to_dict()
-        ov['date'] = str(self.date)
         if ov['visit'] is None:
             del ov['visit']
         return ov
@@ -120,9 +127,13 @@
     @classmethod
     def from_dict(cls, d):
         """Parses the date from a string, and accepts missing visit ids."""
+        d = d.copy()
+        date = d.pop('date')
         return cls(
-            origin=Origin.from_dict(d['origin']),
-            date=dateutil.parser.parse(d['date']),
+            origin=Origin.from_dict(d.pop('origin')),
+            date=(date
+                  if isinstance(date, datetime.datetime)
+                  else dateutil.parser.parse(date)),
             visit=d.get('visit'))
 
 
diff --git a/swh/model/tests/test_hypothesis_strategies.py b/swh/model/tests/test_hypothesis_strategies.py
--- a/swh/model/tests/test_hypothesis_strategies.py
+++ b/swh/model/tests/test_hypothesis_strategies.py
@@ -3,6 +3,8 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+import datetime
+
 import attr
 from hypothesis import given
 
@@ -30,7 +32,8 @@
     elif isinstance(obj, list):
         for value in obj:
             assert_nested_dict(value)
-    elif isinstance(obj, (int, float, str, bytes, bool, type(None))):
+    elif isinstance(obj, (int, float, str, bytes, bool, type(None),
+                          datetime.datetime)):
         pass
     else:
         assert False, obj