Insert-update utf8 string sql server + codeigniter

Small change in SqlSrv driver solves the problem with unicode. Just add _make_unicode function code to /system/database/sqlsrv/sqlsrv_driver.php and replace the code for _insert and _update functions

/**
 * @param mixed $value
 */
function _make_unicode($value){
     if(is_string($value) && $value!="NULL")return "N".$value;
    else return $value;
}

/**
 * Insert statement
 *
 * Generates a platform-specific insert string from the supplied data
 *
 * @access  public
 * @param   string  the table name
 * @param   array   the insert keys
 * @param   array   the insert values
 * @return  string
 */
function _insert($table, $keys, $values)
{
    $values_string = "";
    for($i=0;$i<count($values);$i++){
        if($i==0){
            $values_string.= $this->_make_unicode($values[$i]);
        }else{
            $values_string.= ", ".$this->_make_unicode($values[$i]);
        }
    }
    return "INSERT INTO ".$this->_escape_table($table)." (".implode(', ', $keys).") VALUES ({$values_string})";
}

// --------------------------------------------------------------------

/**
 * Update statement
 *
 * Generates a platform-specific update string from the supplied data
 *
 * @access  public
 * @param   string  the table name
 * @param   array   the update data
 * @param   array   the where clause
 * @param   array   the orderby clause
 * @param   array   the limit clause
 * @return  string
 */
function _update($table, $values, $where)
{
    foreach($values as $key => $val)
    {
       $valstr[] = $key." = ".$this->_make_unicode($val);
    }

    return "UPDATE ".$this->_escape_table($table)." SET ".implode(', ', $valstr)." WHERE ".implode(" ", $where);
}

// --------------------------------------------------------------------

Adding to Alex's answer (sorry not enough reputation to comment). Here are the same functions for CodeIgniter 3.1.1.

_insert_batch

/**
 * Insert batch statement
 *
 * Generates a platform-specific insert string from the supplied data.
 *
 * @param   string  $table  Table name
 * @param   array   $keys   INSERT keys
 * @param   array   $values INSERT values
 * @return  string|bool
 */
protected function _insert_batch($table, $keys, $values)
{
    // Multiple-value inserts are only supported as of SQL Server 2008
    if (version_compare($this->version(), '10', '>='))
    {
        foreach($values as &$value) {
            $value = $this->_make_unicode($value);
        }

        return parent::_insert_batch($table, $keys, $values);
    }

    return ($this->db->db_debug) ? $this->db->display_error('db_unsupported_feature') : FALSE;
}

_update

/**
 * Update statement
 *
 * Generates a platform-specific update string from the supplied data
 *
 * @param   string  $table
 * @param   array   $values
 * @return  string
 */
protected function _update($table, $values)
{
    foreach ($values as &$value) {
        $value = $this->_make_unicode($value);
    }


    $this->qb_limit = FALSE;
    $this->qb_orderby = array();
    return parent::_update($table, $values);
}