public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
        {
            var query = (IQueryable)context.Object;

            var queryString = context.HttpContext.Request.QueryString;
            var columns     = queryString.Value.Contains("$select") ?
                              OutputFormatter.GetPropertiesFromSelect(queryString.Value, query.ElementType) :
                              OutputFormatter.GetProperties(query.ElementType);


            var stream = new MemoryStream();

            using (var document = SpreadsheetDocument.Create(stream, SpreadsheetDocumentType.Workbook))
            {
                var workbookPart = document.AddWorkbookPart();
                workbookPart.Workbook = new Workbook();

                var worksheetPart = workbookPart.AddNewPart <WorksheetPart>();
                worksheetPart.Worksheet = new Worksheet();

                var workbookStylesPart = workbookPart.AddNewPart <WorkbookStylesPart>();
                GenerateWorkbookStylesPartContent(workbookStylesPart);

                var sheets = workbookPart.Workbook.AppendChild(new Sheets());
                var sheet  = new Sheet()
                {
                    Id = workbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "Sheet1"
                };
                sheets.Append(sheet);

                workbookPart.Workbook.Save();

                var sheetData = worksheetPart.Worksheet.AppendChild(new SheetData());

                var headerRow = new Row();

                foreach (var column in columns)
                {
                    headerRow.Append(new Cell()
                    {
                        CellValue = new CellValue(column.Key),
                        DataType  = new EnumValue <CellValues>(CellValues.String)
                    });
                }

                sheetData.AppendChild(headerRow);

                foreach (var item in query)
                {
                    var row = new Row();

                    foreach (var column in columns)
                    {
                        var value       = OutputFormatter.GetValue(item, column.Key);
                        var stringValue = value.ToString();

                        var cell = new Cell();

                        var underlyingType = column.Value.IsGenericType &&
                                             column.Value.GetGenericTypeDefinition() == typeof(Nullable <>) ?
                                             Nullable.GetUnderlyingType(column.Value) : column.Value;

                        var typeCode = Type.GetTypeCode(underlyingType);

                        if (typeCode == TypeCode.DateTime)
                        {
                            if (stringValue != string.Empty)
                            {
                                cell.CellValue = new CellValue()
                                {
                                    Text = DateTime.Parse(stringValue).ToOADate().ToString()
                                };
                                cell.StyleIndex = (UInt32Value)1U;
                            }
                        }
                        else if (typeCode == TypeCode.Boolean)
                        {
                            cell.CellValue = new CellValue(stringValue.ToLower());
                            cell.DataType  = new EnumValue <CellValues>(CellValues.Boolean);
                        }
                        else if (IsNumeric(typeCode))
                        {
                            cell.CellValue = new CellValue(stringValue);
                            cell.DataType  = new EnumValue <CellValues>(CellValues.Number);
                        }
                        else
                        {
                            cell.CellValue = new CellValue(stringValue);
                            cell.DataType  = new EnumValue <CellValues>(CellValues.String);
                        }

                        row.Append(cell);
                    }

                    sheetData.AppendChild(row);
                }


                workbookPart.Workbook.Save();
            }

            if (stream?.Length > 0)
            {
                stream.Seek(0, SeekOrigin.Begin);
            }

            return(stream.CopyToAsync(context.HttpContext.Response.Body));
        }
 public static IEnumerable <KeyValuePair <string, Type> > GetProperties(Type type)
 {
     return(type.GetProperties(BindingFlags.Public | BindingFlags.Instance)
            .Where(p => p.CanRead && OutputFormatter.IsSimpleType(p.PropertyType)).Select(p => new KeyValuePair <string, Type>(p.Name, p.PropertyType)));
 }