Add uid to storage.update_experiment

Why:

`storage.fetch_experiments` returns documents, not `Experiment` objects.
This makes it complicated to just fetch and update an experiment given
that `update_experiment` expects an `Experiment` object.

src/orion/storage/base.py

@@ -35,13 +35,16 @@ def create_experiment(self, config):
         """Insert a new experiment inside the database"""
         raise NotImplementedError()
 
-    def update_experiment(self, experiment, where=None, **kwargs):
+    def update_experiment(self, experiment=None, uid=None, where=None, **kwargs):
         """Update a the fields of a given trials
 
         Parameters
         ----------
-        experiment: Experiment
-            Experiment object to update
+        experiment: Experiment, optional
+           experiment object to retrieve from the database
+
+        uid: str, optional
+            experiment id used to retrieve the trial object
 
         where: Optional[dict]
             constraint experiment must respect
@@ -53,6 +56,14 @@ def update_experiment(self, experiment, where=None, **kwargs):
         -------
         returns true if the underlying storage was updated
 
+        Raises
+        ------
+        UndefinedCall
+            if both experiment and uid are not set
+
+        AssertionError
+            if both experiment and uid are provided and they do not match
+
         """
         raise NotImplementedError()
 

src/orion/storage/legacy.py

@@ -91,12 +91,21 @@ def create_experiment(self, config):
         """See :func:`~orion.storage.BaseStorageProtocol.create_experiment`"""
         return self._db.write('experiments', data=config, query=None)
 
-    def update_experiment(self, experiment, where=None, **kwargs):
+    def update_experiment(self, experiment=None, uid=None, where=None, **kwargs):
         """See :func:`~orion.storage.BaseStorageProtocol.update_experiment`"""
+        if experiment is not None and uid is not None:
+            assert experiment._id == uid
+
+        if uid is None:
+            if experiment is None:
+                raise MissingArguments('Either `experiment` or `uid` should be set')
+
+            uid = experiment._id
+
         if where is None:
             where = dict()
 
-        where['_id'] = experiment._id
+        where['_id'] = uid
         return self._db.write('experiments', data=kwargs, query=where)
 
     def fetch_experiments(self, query, selection=None):

tests/unittests/storage/test_storage.py

@@ -151,6 +151,32 @@ def test_fetch_experiments(self, storage, name='0', user='a'):
             experiments = storage.fetch_experiments({'name': '-1', 'metadata.user': user})
             assert len(experiments) == 0
 
+    def test_update_experiment(self, monkeypatch, storage, name='0', user='a'):
+        """Test fetch experiments"""
+        with OrionState(experiments=generate_experiments(), database=storage) as cfg:
+            storage = cfg.storage()
+
+            class _Dummy():
+                pass
+
+            experiment = cfg.experiments[0]
+            mocked_experiment = _Dummy()
+            mocked_experiment._id = experiment['_id']
+
+            storage.update_experiment(mocked_experiment, test=True)
+            assert storage.fetch_experiments({'_id': experiment['_id']})[0]['test']
+            assert 'test' not in storage.fetch_experiments({'_id': cfg.experiments[1]['_id']})[0]
+
+            storage.update_experiment(uid=experiment['_id'], test2=True)
+            assert storage.fetch_experiments({'_id': experiment['_id']})[0]['test2']
+            assert 'test2' not in storage.fetch_experiments({'_id': cfg.experiments[1]['_id']})[0]
+
+            with pytest.raises(MissingArguments):
+                storage.update_experiment()
+
+            with pytest.raises(AssertionError):
+                storage.update_experiment(experiment=mocked_experiment, uid='123')
+
     def test_register_trial(self, storage):
         """Test register trial"""
         with OrionState(experiments=[base_experiment], database=storage) as cfg: