Excel exports in .NET Core using ClosedXML

ClosedXML makes Excel exports straightforward in .NET without requiring Excel installation. Perfect for generating reports from any IEnumerable collection.

Install package

dotnet add package ClosedXML

Basic export to file

The simplest way to export any objects to Excel using ClosedXML’s InsertTable<T>() method:

IEnumerable<AuthorDto> items = GetAuthors();

using var wb = new XLWorkbook();
var ws = wb.AddWorksheet();

// Inserts the collection to Excel as a table with a header row.
ws.Cell("A1").InsertTable(items);

// Adjust column size to contents.
ws.Columns().AdjustToContents();

// Save to local file system.
var filename = $"Export - {DateTime.UtcNow:yyyyMMddHHmmss}.xlsx";
wb.SaveAs(filename);

ASP.NET Core minimal API endpoint

Complete minimal API endpoint that returns a downloadable Excel file:

app.MapGet("/export/authors", (IAuthorService authorService) =>
{
    var authors = authorService.GetAuthors();
    
    using var wb = new XLWorkbook();
    var ws = wb.AddWorksheet();
    ws.Cell("A1").InsertTable(authors);
    ws.Columns().AdjustToContents();

    using var stream = new MemoryStream();
    wb.SaveAs(stream);
    var content = stream.ToArray();
    var contentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
    var filename = $"Authors - {DateTime.UtcNow:yyyyMMddHHmmss}.xlsx";

    return Results.File(content, contentType, filename);
});

Example class

The AuthorDto can be any C# class object:

public class AuthorDto
{
    public int Id { get; set; }
    public string? FirstName { get; set; }
    public string? LastName { get; set; }
    public string? ContactEmail { get; set; } = "";
}

This approach works well for simple exports. For advanced table customization, check the tables feature in the official docs.