(并非全部）数据可以'；无法访问数据库

我想将数据发送到我的数据库(group_id、user_id和group_name(，但只有前两个数据进入了数据库。当我var_dump $groupinvitation->Invitation_group_name = mysql_real_escape_string($groupname);时，它会给我正确的group_name。我做错了什么？

当我用一个随机单词替换'" . $db->conn->real_escape_string($this->Invitation_group_name) . "'时，它运行良好。。

PHP

$groupinvitation = new GroupInvitation();
if (isset($_POST["Accept"])) {
    try {
        $group_id = mysql_real_escape_string($_POST["group_id"]);
        $groupinfo = $group->GetGroupInfoByGroupId($group_id);
        $groupname = $groupinfo['group_name'];
        $requestnumber = mysql_real_escape_string($_POST['acceptID']);
        $groupinvitation->AddAsGroupMember($number, $group_id);
        $groupinvitation-> AcceptGroupRequest($requestnumber);
        $groupinvitation->Invitation_group_name = mysql_real_escape_string($groupname);
        $feedback = "Awesome, You just added a friend!";

    } catch(Exception $e) {
        $feedback = $e -> getMessage();
    }
}

声明：

class GroupInvitation
    {
    private $m_sGroup_invitation_group_name;

        public function __set($p_sProperty, $p_vValue)
        {
            switch($p_sProperty)
            {
                case "Invitation_group_name":
                $this->m_sGroup_invitation_group_name = $p_vValue;
                break;
            }
        }
        public function __get($p_sProperty)
        {
            switch($p_sProperty)
            {
                case "Invitation_group_name":
                return $this->m_sGroup_invitation_group_name ;
                break;
            }
        }

函数：

public function AddAsGroupMember($number, $group_id)
        {
                $db = new Db();
                $insert = "INSERT INTO tblgroup_member(

                                group_id,
                                user_id,
                                group_name
                          ) VALUES (
                                '" . $db->conn->real_escape_string($group_id) . "',
                                '" . $db->conn->real_escape_string($number) . "',
                                '" . $db->conn->real_escape_string($this->Invitation_group_name) . "'   

                          )";
                $db->conn->query($insert);

        }