public class Sheet1
{
    public DateTime Date { get; set; }
    public int Quantity { get; set; }
    public string Description { get; set; }
    public decimal Amount { get; set;}
    public decimal Total { get; set; }
    public string Notes { get; set; }
}

public class TestFileContext : ExcelContext
{
    // in order to read files, you'll need one of these constructors
    public TestFileContext(System.IO.Stream stream) : base(stream) { }
    public TestFileContext(string filename) : base(filename) { }
    public TestFileContext(ExcelPackage excelPackage) : base(excelPackage) { }

    // in order to write new files, you'll need a default constructor
    public TestFileContext() : base() { }

    // define an easy way to access the sheet1 table
    public List<Sheet1> Sheet1 => GetSheet<Sheet1>();

    protected override void OnModelCreating(ExcelModelBuilder builder)
    {
        builder.IgnoreSheetNames();             // ignore sheet names; just take the first sheet
        
        var sheet1 = builder.Sheet<Sheet1>();
        sheet1.Column(x => x.Date);             // define a column for the Date property; look for a column with the name "Date"
        sheet1.Column(x => x.Quantity, "Qty");  // for Quantity, look for a column with the name "Qty"
        sheet1.Column(x => x.Description)       // for Description, look for a column named either "Description" or "Desc"
            .AlternateName("Desc");
        sheet1.Column(x => x.Amount);
        sheet1.Column(x => x.Total);
        sheet1.Column(x => x.Notes)
            .Optional();                        // optional columns are not required to be in the Excel workbook

        sheet1.SkipEmptyRows();                 // skip empty rows when reading
    }
}

var context = new TestFileContext(filename);
foreach (var row in context.Sheet1) {
    // do something with the row
}

var context = new TestFileContext();

// add some data to the context
context.Sheet1.Add(new Sheet1 {
    Date = DateTime.Now,
    Quantity = 1,
    Description = "Test",
    Amount = 1.00m,
    Total = 1.00m,
    Notes = "Test"
});

context.SerializeToFile(filename);

public class TestFileContext : ExcelContext
{
    // in order to read files, you'll need one of these constructors
    public TestFileContext(System.IO.Stream stream) : base(stream) { }
    public TestFileContext(string filename) : base(filename) { }
    public TestFileContext(ExcelPackage excelPackage) : base(excelPackage) { }

    // in order to write new files, you'll need a default constructor
    public TestFileContext() : base() { }

    // define an easy way to access the sheets by name
    public List<Sheet1> Sheet1 => GetSheet<Sheet1>();
    public List<MyClass2> Sheet2 => GetSheet<MyClass2>();
        
    protected override void OnModelCreating(ExcelModelBuilder builder)
    {
        // set up a formatter for the header row
        Action<ExcelRange> headerFormatter = range => {
            range.Style.HorizontalAlignment = OfficeOpenXml.Style.ExcelHorizontalAlignment.Center;
            range.Style.Border.Bottom.Style = OfficeOpenXml.Style.ExcelBorderStyle.Thin;
        };
        // set up a formatter for number cells
        Action<ExcelRange> numberFormatter = range => range.Style.Numberformat.Format = "#,##0.00";

        // define a sheet which should be called "Sheet1" in the workbook (name inferred from the class name)
        var sheet1 = builder.Sheet<Sheet1>();

        // define a column called "Date" (it can appear in any order in the sheet; it does not
        // have to be first; but when saving they will save in the order defined)
        sheet1.Column(x => x.Date)
            // apply the header formatter to the header row, which adds a thin line under the header text
            .HeaderFormatter(headerFormatter)
            // apply a date format to cells in this column
            .ColumnFormatter(range => range.Style.Numberformat.Format = "MM/dd/yyyy");
            
        sheet1.Column(x => x.Quantity)
            .HeaderFormatter(headerFormatter)
            // here we are centering the data in this column
            .ColumnFormatter(range => range.Style.HorizontalAlignment = OfficeOpenXml.Style.ExcelHorizontalAlignment.Center);

        sheet1.Column(x => x.Description)
            .HeaderFormatter(headerFormatter);

        sheet1.Column(x => x.Amount)
            .HeaderFormatter(headerFormatter)
            .ColumnFormatter(numberFormatter);   // use our number format defined above

        sheet1.Column(x => x.Total)
            // here instead of writing the value, we write a forumla to these cells that multiplies the quantity times the amount
            .WriteSerializer((range, value) => {
                var sheet = range.Worksheet;
                var qtyAddress = sheet.Cells[range.Start.Row, 2].Address;
                var amountAddress = sheet.Cells[range.Start.Row, 4].Address;
                range.Formula = $"{qtyAddress}*{amountAddress}";
            })
            // we still apply formatting to the header and data cells
            .HeaderFormatter(headerFormatter)
            .ColumnFormatter(numberFormatter)
            // when complete with this column, we are adding a sum at the bottom of the page
            .WritePolisher(range => {
                range = range[range.Start.Row + 1, range.Start.Column, range.End.Row + 1, range.End.Column];
                var totalRange = range.Worksheet.Cells[range.End.Row + 1, range.End.Column];
                totalRange.Formula = $"SUM({range.Address})";
                totalRange.Style.Numberformat.Format = "$ #,##0.00";
                range[totalRange.Start.Row, totalRange.Start.Column - 1].Value = "Total";
            });

        sheet1.Column(x => x.Notes)
            .HeaderFormatter(headerFormatter)
            .Optional();

        // anticipate that there may be a header at the top of the sheet; so determine the range to read
        // from by looking for the first cell in column A that contains the word "Date"
        sheet1.ReadRangeLocator(worksheet => {
            // skip header rows on this sheet
            for (int i = 1; i <= worksheet.Dimension.Rows; i++) {
                if (worksheet.Cells[i, 1].Text == "Date") {
                    return worksheet.Cells[i, 1, worksheet.Dimension.End.Row, worksheet.Dimension.End.Column];
                }
            }
            return null;
        });

        sheet1.SkipEmptyRows();

        // when writing, we want to skip the first two rows
        sheet1.WriteRangeLocator(worksheet => worksheet.Cells[3, 1]);

        // when finishing writing, we can add additional operations
        sheet1.WritePolisher((worksheet, range) => {
            // recalculate the sheet
            worksheet.Calculate();
            // auto-size the column widths
            for (int col = 1; col <= worksheet.Dimension.End.Column; col++) {
                var column = worksheet.Column(col);
                column.AutoFit();
                column.Width *= 1.2;
            }
            // add a header to the page
            worksheet.Cells[1, 1].Value = "This is a test header";
        });

        // we can also define additional sheets in the same workbook

        // here we define a sheet which should be called "Sheet2" in the workbook
        var sheet2 = builder.Sheet<MyClass2>("Sheet2");
        // todo: define some columns for MyClass2 here
    }

    // we can define additional logic when reading rows
    protected override object OnReadRow(ExcelRange range, ISheetModel model, IColumnModel[] columnMapping)
    {
        //skip rows where the first column is blank
        if (range.Worksheet.Cells[range.Start.Row, 1].Value == null)
            return null;

        return base.OnReadRow(range, model, columnMapping);
    }

    // we can define additional logic when writing the workbook
    protected override void OnWriteFile(ExcelWorkbook workbook)
    {
        base.OnWriteFile(workbook);

        // just a sample; we already calculated the workbook within the write polisher
        workbook.Calculate();
    }
}