FOSUserBundle: username vs usernameCanonical

Question

Why does the FOSUserBundle User entity have two properties for a username (and other fields)?

/**  * @var string  */ protected $username;  /**  * @var string  */ protected $usernameCanonical; 

I've read the docs, browsed the source code, and tried to search for information, and I can't find out why it exists. It seems to always store the same values. I'm sure there is a good reason, can someone fill me in?

Answer 1

Canonical fields get lowercased before comparison or search — to make sure there are no duplicates with the same value but with different case like [email protected] and [email protected].