How to parse excel rows back to types using EPPlus

Question

EPPlus has a convenient LoadFromCollection<T> method to get data of my own type into a worksheet.

For example if I have a class:

public class Customer
{
    public int Id { get; set; }
    public string Firstname { get; set; }
    public string Surname { get; set; }
    public DateTime Birthdate { get; set; }
}

Then the following code:

var package = new ExcelPackage();
var sheet = package.Workbook.Worksheets.Add("Customers");
var customers = new List<Customer>{
    new Customer{
        Id = 1,
        Firstname = "John",
        Surname = "Doe",
        Birthdate = new DateTime(2000, 1, 1)
    },
    new Customer{
        Id = 2,
        Firstname = "Mary",
        Surname = "Moe",
        Birthdate = new DateTime(2001, 2, 2)
    }
};
sheet.Cells[1, 1].LoadFromCollection(customers);
package.Save();

...will add 2 rows to a worksheet called "Customers".

My question is if there is a convenient counterpart to extract the rows from excel (for example after some modifications have been made) back into my types.

Something like:

var package = new ExcelPackage(inputStream);
var customers = sheet.Dimension.SaveToCollection<Customer>() ??

I have

• been looking through the EPPlus codebase
• searched for any saving questions
• searched for any parsing questions
• seen this question on reading single cells

... but found nothing on how to simply parse the rows to my type.

Answer 1

Inspired by the above I took it a slightly different route.

1. I created an attribute and mapped each property to a column.
2. I use the DTO type to define what I expect each column to be
3. Allow columns to not be requried
4. Use EPPlus to convert the types

By doing so it allows me to use traditional model validation, and embrace changes to column headers

-- Usage:

using(FileStream fileStream = new FileStream(_fileName, FileMode.Open)){
      ExcelPackage excel = new ExcelPackage(fileStream);
      var workSheet = excel.Workbook.Worksheets[RESOURCES_WORKSHEET];

      IEnumerable<ExcelResourceDto> newcollection = workSheet.ConvertSheetToObjects<ExcelResourceDto>();
      newcollection.ToList().ForEach(x => Console.WriteLine(x.Title));
 }

Dto that maps to excel

public class ExcelResourceDto
{
    [Column(1)]
    [Required]
    public string Title { get; set; }

    [Column(2)]
    [Required]
    public string SearchTags { get; set; }
}

This is the attribute definition

[AttributeUsage(AttributeTargets.All)]
public class Column : System.Attribute
{
    public int ColumnIndex { get; set; }


    public Column(int column) 
    {
        ColumnIndex = column;
    }
} 

Extension class to handle mapping rows to DTO

public static class EPPLusExtensions
{
   public static IEnumerable<T> ConvertSheetToObjects<T>(this ExcelWorksheet worksheet) where T : new()
    {

        Func<CustomAttributeData, bool> columnOnly = y => y.AttributeType == typeof(Column);

        var columns = typeof(T)
                .GetProperties()
                .Where(x => x.CustomAttributes.Any(columnOnly))
        .Select(p => new
        {
            Property = p,
            Column = p.GetCustomAttributes<Column>().First().ColumnIndex //safe because if where above
        }).ToList();


        var rows= worksheet.Cells
            .Select(cell => cell.Start.Row)
            .Distinct()
            .OrderBy(x=>x);


        //Create the collection container
        var collection = rows.Skip(1)
            .Select(row =>
            {
                var tnew = new T();
                columns.ForEach(col =>
                {
                    //This is the real wrinkle to using reflection - Excel stores all numbers as double including int
                    var val = worksheet.Cells[row, col.Column];
                    //If it is numeric it is a double since that is how excel stores all numbers
                    if (val.Value == null)
                    {
                        col.Property.SetValue(tnew, null);
                        return;
                    }
                    if (col.Property.PropertyType == typeof(Int32))
                    {
                        col.Property.SetValue(tnew, val.GetValue<int>());
                        return;
                    }
                    if (col.Property.PropertyType == typeof(double))
                    {
                        col.Property.SetValue(tnew, val.GetValue<double>());
                        return;
                    }
                    if (col.Property.PropertyType == typeof(DateTime))
                    {
                        col.Property.SetValue(tnew, val.GetValue<DateTime>());
                        return;
                    }
                    //Its a string
                    col.Property.SetValue(tnew, val.GetValue<string>());
                });

                return tnew;
            });


        //Send it back
        return collection;
    }
}