Excel exports in .NET Core using ClosedXML

Aug 12, 2023
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2 min read
•
ASP.NET Core •
Code Snippet

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.