mo.db: Správný default pro UserRole.assigned_at

mo/db.py

@@ -279,7 +279,7 @@ class UserRole(Base):
     year = Column(Integer)
     seq = Column(Integer)
     assigned_by = Column(Integer, ForeignKey('users.user_id'))
-    assigned_at = Column(DateTime(True))
+    assigned_at = Column(DateTime(True), nullable=False, server_default=text("CURRENT_TIMESTAMP"))
 
     user = relationship('User', primaryjoin='UserRole.user_id == User.user_id')
     assigned_by_user = relationship('User', primaryjoin='UserRole.assigned_by == User.user_id')