Why does my younger brother always prompt that the deletion fails? Where is the question? I hope you can help me with the following code:

Why does my deletion function always prompt that the deletion fails? Where is the question? I hope you can use the code functiondelete ($ id = null) {& nbsp; if (! $ Id) {& nbsp; $ this-& gt; Session-& gt; s why does my deletion function always prompt deletion failure? Where is the question? I hope you can help me with the following code:
Function delete ($ id = null ){

If (! $ Id ){
$ This-> Session-> setFlash ('invalid', true );
}

Else if ($ this-> User-> del ($ id )){

$ This-> Session-> setFlash ('deleted', true );
}
Else {
$ This-> Session-> setFlash ('could not delete', true );
}
$ This-> redirect (array ('action' => 'userlist '));
}


------ Solution --------------------
But it still enters the else branch. If you cannot delete the code, it indicates that there is a problem with the deletion code. $ This-> User-> del (); how is this function written?