[OpenXml] Read/Write row/cell from excel

public static void test(){
using (SpreadsheetDocument document = SpreadsheetDocument.Open("test.xlsx", true))
{
WorkbookPart workbookPart = document.WorkbookPart;

string relId = workbookPart.Workbook.Descendants<Sheet>().First(sheet => sheet.Name.Value.ToLower().Equals("sheet1")).Id;
WorksheetPart worksheetpart = (WorksheetPart)workbookPart.GetPartById(relId);

DocumentFormat.OpenXml.Spreadsheet.Worksheet worksheet = worksheetpart.Worksheet;
SheetData sheetData = worksheet.GetFirstChild<SheetData>();

for (int i = 2; i <= 3; i++)
{
Row row = new Row() { RowIndex = (uint)i };
row.Append(new Cell() { CellReference = "A" + i, DataType = CellValues.String, CellValue = new CellValue("kaka") });//, StyleIndex = styleIndex });
row.Append(new Cell() { CellReference = "B" + i, DataType = CellValues.String, CellValue = new CellValue("2") });//, StyleIndex = styleIndex });
row.Append(new Cell() { CellReference = "C" + i, DataType = CellValues.String, CellValue = new CellValue("GENERAL MANAGEMENT") });//, StyleIndex = styleIndex });
row.Append(new Cell() { CellReference = "D" + i, DataType = CellValues.String, CellValue = new CellValue("2") });//, StyleIndex = styleIndex });
row.Append(new Cell() { CellReference = "E" + i, DataType = CellValues.String, CellValue = new CellValue((1 == 1).ToString()) });//, StyleIndex = styleIndex });
sheetData.Append(row);
}

// loop each row to get value;
string cellValue = GetCellValue(sheetData.Descendants<Row>().ElementAt<Row>(0), "A", getSharedString(document));

worksheet.Save();
}
}

private static List<SharedStringItem> getSharedString(SpreadsheetDocument document)
{
WorkbookPart workbookPart = document.WorkbookPart;
return workbookPart.SharedStringTablePart.SharedStringTable.Elements<SharedStringItem>().ToList<SharedStringItem>();
}

// cell could be null
private static Cell GetCell(Row row, string columnName)
{
return row.Descendants<Cell>().FirstOrDefault(p => p.CellReference == columnName + row.RowIndex);
}

// call getSharedString
// call GetCell
// => retrieve cell value
public static string GetCellValue(Row row, string columnName, List<SharedStringItem> sharedStrings)
{
Cell cell = GetCell(row, columnName);

if (cell == null)
{
return null;
}

string value = "";

if (cell.DataType != null && cell.DataType.Value == CellValues.SharedString)
{
SharedStringItem item = sharedStrings.ElementAt<SharedStringItem>(Int32.Parse(cell.CellValue.Text));
value = item.InnerText;
}
else
{
value = cell.CellValue.Text;
}
return value;
}