$this->db->error()

First, the insert() method returns false on an error, so you can start by checking the returned value. Then, you can check the $error['code'] value and redirect to instruments/duplicate if it matches your error code. If you haven't redirected yet, you can return the $error['message'] if it is set. Finally, you can redirect to instruments/addFail, since you have no other options in your original code.

PHP Code:

if ($this->db->insert('instrument', $data)) {
    redirect('instruments/addSuccess');
}

$error = $this->db->error();
if ($error['code'] == 1062) {
    redirect('instruments/duplicate');
}

if (isset($error['message'])) {
    return $error['message'];
}

redirect('instruments/addFail'); 


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