diff --git a/calsocial/models.py b/calsocial/models.py
index b4312fe..b61d502 100644
--- a/calsocial/models.py
+++ b/calsocial/models.py
@@ -597,19 +597,21 @@ class Invitation(db.Model):  # pylint: disable=too-few-public-methods
     """
 
     __tablename__ = 'invitations'
+    # pylint: disable=invalid-name
+    id = db.Column(db.Integer(), primary_key=True)
 
     #: The ID of the sender’s profile
-    sender_id = db.Column(db.Integer(), db.ForeignKey('profiles.id'), primary_key=True)
+    sender_id = db.Column(db.Integer(), db.ForeignKey('profiles.id'), index=True)
 
     sender = db.relationship('Profile', foreign_keys=[sender_id])
 
     #: The ID of the invitee’s profile
-    invitee_id = db.Column(db.Integer(), db.ForeignKey('profiles.id'), primary_key=True)
+    invitee_id = db.Column(db.Integer(), db.ForeignKey('profiles.id'), index=True)
 
     invitee = db.relationship('Profile', foreign_keys=[invitee_id])
 
     #: The ID of the event
-    event_id = db.Column(db.Integer(), db.ForeignKey('events.id'), primary_key=True)
+    event_id = db.Column(db.Integer(), db.ForeignKey('events.id'), index=True)
 
     event = db.relationship('Event', backref=db.backref('invitations', lazy='dynamic'))