insert_id() not returning

[eluser]Gyzm[/eluser]
I just encountered this same issue and it took me about a little bit to figure out what the issue was.

In my case it was the session class. That seems odd right? Well, it's not when you're storing your session in the database.

I was setting some flash data prior to calling

Code:

$this->db->insert_id()

and the result of which was always 0.

Return values of mysql_insert_id:

"The ID generated for an AUTO_INCREMENT column by the previous query on success, 0 if the previous query does not generate an AUTO_INCREMENT value, or FALSE if no MySQL connection was established." - php.net

The ci_session table's primary key is not set to auto_increment. With the session update being the last write operation that occurred on my DB it made perfect sense why I kept getting 0.

Hope that helps someone.