CSV Export

Return CsvResponse<TRow> directly from HandleAsync. It implements IResult, so the framework streams the rows to the response without buffering the entire dataset in memory.

public sealed class UserExportRow
{
    [Name("id")]    public int    Id    { get; init; }
    [Name("name")]  public string Name  { get; init; } = string.Empty;
    [Name("email")] public string Email { get; init; } = string.Empty;
}

public sealed class ExportUsersEndpoint : IEndpoint<CsvResponse<UserExportRow>>
{
    private readonly IUserRepository _repository;

    public ExportUsersEndpoint(IUserRepository repository) => _repository = repository;

    public void Configure(IEndpointConfiguration config)
    {
        config.Get("/users/export").Summary("Export users as CSV");
    }

    public Task<CsvResponse<UserExportRow>> HandleAsync(CancellationToken cancel)
    {
        // IAsyncEnumerable<T> is written row-by-row without loading everything into memory.
        var rows = _repository.GetAllAsync(cancel);
        return Task.FromResult(CsvResponse.From(rows, fileName: "users.csv"));
    }
}

CsvResponse.From also accepts IEnumerable<T> for synchronous sequences.

CsvResponse.From Parameters

CsvResponse.From accepts the following parameters:

Parameter	Type	Default	Description
rows	IAsyncEnumerable<TRow> or IEnumerable<TRow>	(required)	Sequence of rows to write as CSV
classMap	ClassMap?	null	Column mapping and formatting configuration through CsvHelper ClassMap. If null, CsvHelper convention-based mapping and attributes on TRow are used
fileName	string	"export.csv"	File name written to the Content-Disposition header
statusCode	HttpStatusCode	HttpStatusCode.OK	HTTP status code
configuration	CsvConfiguration?	null	CsvHelper writer configuration. If null, the default configuration using CultureInfo.InvariantCulture is applied

// Example with all parameters specified
CsvResponse.From(
    rows,
    classMap: new UserRowMap(),
    fileName: "users-export.csv",
    statusCode: HttpStatusCode.OK,
    configuration: new CsvConfiguration(CultureInfo.InvariantCulture)
    {
        Delimiter = "\t"
    }
);

For custom column mapping on export, see Class Map.