when inserting any data in a component development always use JTable class. This will ensure that the id in the table _assets will get inserted and there will be secured ACL functionality.
Two important functions are table->bind and table->save
To know more about ACL please have a look at our link http://www.joomla25upgrade.com/joomla-25-tutorials/34-acl-administration-in-action.html.
Reference : http://docs.joomla.org/Using_the_JTable_class