diff --git a/timely_beliefs/beliefs/classes.py b/timely_beliefs/beliefs/classes.py
index 9715d1be..dfee9393 100644
--- a/timely_beliefs/beliefs/classes.py
+++ b/timely_beliefs/beliefs/classes.py
@@ -28,6 +28,7 @@
     func,
     select,
 )
+from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.ext.declarative import declared_attr
 from sqlalchemy.ext.hybrid import hybrid_method, hybrid_property
 from sqlalchemy.orm import Session, backref, declarative_mixin, relationship
@@ -251,7 +252,7 @@ def add_to_session(
         beliefs_data_frame: "BeliefsDataFrame",
         expunge_session: bool = False,
         allow_overwrite: bool = False,
-        bulk_save_objects: bool = False,
+        bulk_save_objects: bool = True,
         commit_transaction: bool = False,
     ):
         """Add a BeliefsDataFrame as timed beliefs to a database session.
@@ -274,23 +275,53 @@ def add_to_session(
                                     if False, you can still add other data to the session
                                     and commit it all within an atomic transaction
         """
+        if beliefs_data_frame.empty:
+            return
         # Belief timing is stored as the belief horizon rather than as the belief time
-        belief_records = (
-            beliefs_data_frame.convert_index_from_belief_time_to_horizon()
-            .reset_index()
-            .to_dict("records")
+        beliefs_data_frame = (
+            beliefs_data_frame.convert_index_from_belief_time_to_horizon().reset_index()
         )
-        beliefs = [cls(sensor=beliefs_data_frame.sensor, **d) for d in belief_records]
+        beliefs = [
+            cls(sensor=beliefs_data_frame.sensor, **d)
+            for d in beliefs_data_frame.to_dict("records")
+        ]
+
         if expunge_session:
             session.expunge_all()
-        if not allow_overwrite:
-            if bulk_save_objects:
-                session.bulk_save_objects(beliefs)
+
+        if bulk_save_objects:
+            # serialize source and sensor
+            beliefs_data_frame["source_id"] = beliefs_data_frame["source"].apply(
+                lambda x: x.id
+            )
+            beliefs_data_frame["sensor_id"] = beliefs_data_frame.sensor.id
+            beliefs_data_frame = beliefs_data_frame.drop(columns=["source"])
+
+            smt = insert(cls).values(beliefs_data_frame.to_dict("records"))
+
+            if allow_overwrite:
+                smt = smt.on_conflict_do_update(
+                    index_elements=[
+                        "event_start",
+                        "belief_horizon",
+                        "source_id",
+                        "sensor_id",
+                        "cumulative_probability",
+                    ],
+                    set_=dict(event_value=smt.excluded.event_value),
+                )
             else:
-                session.add_all(beliefs)
+                smt = smt.on_conflict_do_nothing()
+
+            session.execute(smt)
+
         else:
-            for belief in beliefs:
-                session.merge(belief)
+            if allow_overwrite:
+                for belief in beliefs:
+                    session.merge(belief)
+            else:
+                session.add_all(beliefs)
+
         if commit_transaction:
             session.commit()
 
diff --git a/timely_beliefs/tests/test_belief_persistence.py b/timely_beliefs/tests/test_belief_persistence.py
index da4eb8d2..5bdce7de 100644
--- a/timely_beliefs/tests/test_belief_persistence.py
+++ b/timely_beliefs/tests/test_belief_persistence.py
@@ -49,9 +49,31 @@ def test_adding_to_session(
     assert len(bdf) == len(new_bdf)
 
 
-@pytest.mark.parametrize("bulk_save_objects", [False, True])
-def test_fail_adding_to_session(
-    bulk_save_objects: bool,
+def test_adding_to_session_succeeds(
+    time_slot_sensor: DBSensor,
+    rolling_day_ahead_beliefs_about_time_slot_events,
+):
+
+    # Retrieve some data from the database
+    bdf = DBTimedBelief.search_session(
+        session=session,
+        sensor=time_slot_sensor,
+    )
+
+    # Attempting to save the same data should not fail, even if we expunge everything from the session
+    try:
+        DBTimedBelief.add_to_session(
+            session,
+            bdf,
+            expunge_session=True,
+            bulk_save_objects=True,
+            commit_transaction=True,
+        )
+    except IntegrityError as exception:
+        raise pytest.fail("DID RAISE {0}".format(exception))
+
+
+def test_adding_to_session_fails(
     time_slot_sensor: DBSensor,
     rolling_day_ahead_beliefs_about_time_slot_events,
 ):
@@ -68,6 +90,6 @@ def test_fail_adding_to_session(
             session,
             bdf,
             expunge_session=True,
-            bulk_save_objects=bulk_save_objects,
+            bulk_save_objects=False,
             commit_transaction=True,
         )