Cell index must be >= 0

[Burak Karakaya]

var excelData = mapper.Take<CustomNpoiModel>(mapper.Workbook.GetSheetAt(0).SheetName).Select(x => x.Value).ToList();

I have used this line in 10 different "Actions" and every single approach this mapping works great, but in my last action I got this strange exception which is "Cell index must be >= 0" and the error does not provide any additional information!

Strangely, I have tried to use an Excel File which I've created last week, and when I use that File, I didn't get any errors,
then I simply copy that Excel file and create a new one, and copy those rows into the new Excel File, and yet I got the same error.

Additional Information :

public class CustomNpoiModel 
{
      [Column("No")]
      public int No { get; set; }
      
      [Column("Name")]
      public string Name { get; set; }
   
      [Column("Path")]
      public string Path { get; set; }
}

[Burak Karakaya]

At least please send the InnerException.

Still need information on this!

[Donny Tian]

Hi, if you can upload the file (with dummy values) and paste your code snippet, that will help me a lot, thanks!

[Burak Karakaya]

Hello Mr.Donny,

The problem is that this issue is not reproducible.

You can download the simple excel from here basic-excel

Basically, as I mentioned above,

I have a model like below

public class ExcelService 
{
        public void ImportFromExcel(IFormFile excelFile)
        {
              var excelData = mapper.Take<CustomNpoiModel>(mapper.Workbook.GetSheetAt(0).SheetName)
                                    .Select(x => x.Value).ToList();

              excelData.ForEach(data => {
                   var product = new Product
                   {
                          No = data.No,
                          Name = data.Name,
                          Path = data.Path
                   };
                   _context.Products.Add(product);
                   _context.SaveChanges();
              });
        }
}
public class CustomNpoiModel 
{
      [Column("No")]
      public int No { get; set; }
      
      [Column("Name")]
      public string Name { get; set; }
   
      [Column("Path")]
      public string Path { get; set; }
}

var excelData = mapper.Take<CustomNpoiModel>(mapper.Workbook.GetSheetAt(0).SheetName).Select(x => x.Value).ToList();

I am simply importing the data from excel file, then I am updating the rows of the excel file everytime when I have to import new data, but sometimes I am getting this exception from this line.

And also the exception has no "InnerException"

[Donny Tian]

hi, seems the file format is invalid, neither NPOI nor my local Office365 can open it.

[Donny Tian]

But I will include more error details for any exception during import.

[Burak Karakaya]

Thank you!

[Burak Karakaya]

Hello Donny,

It seems that when you construct a mapper as Mapper mapper = new Mapper(stream), sometimes it creates mapper.FirstRowIndex value is set to -1. So, when you explicitly set it to 0 as mapper.FirstRowIndex = 0, the problem is solving.

I have created a new & small helper library for empty cells detection of a sheet and sets the headers & _firstRowIndex, I can share it with you if you want to.

[Donny Tian]

ok, this property may mislead users to get the value after constructing a mapper. Actually it is initialized as -1 by design. The purpose of this property is to let user specify for the first row so the mapper can start to work from that row, even if there are non-blank rows above that index. for example you may have description rows at the beginning rows, and data rows just start after that.

public int FirstRowIndex { get; set; } = -1;

If you set it as zero explicitly, means there is no header row, the first row is data row already. if mapper see it's -1 then mapper will use default value sheet.FirstRowNum.

private int GetFirstRowIndex(ISheet sheet) =>
    FirstRowIndex >= 0 ? FirstRowIndex : sheet.FirstRowNum;

I don't see any issue with -1 as the default value, your exception may be related to the column index rather than the row index.
Or may already been fixed :)