Set datetime url format to ISO8601

[lucasteles]

Is there any way to define all datetime format to iso8601? (date.ToString("o", CultureInfo.InvariantCulture))

[glennawatson]

Two options:

Per-parameter via the Query attribute Format property:

[Get("/events")]
Task GetEvents([Query(Format = "o")] DateTime from);

Global, for every DateTime in URLs - implement IUrlParameterFormatter and set it on RefitSettings:

class Iso8601UrlParameterFormatter : DefaultUrlParameterFormatter
{
    public override string? Format(object? value, ICustomAttributeProvider attributeProvider, Type type)
    {
        if (value is DateTime dt)
            return dt.ToString("o", CultureInfo.InvariantCulture);
        if (value is DateTimeOffset dto)
            return dto.ToString("o", CultureInfo.InvariantCulture);
        return base.Format(value, attributeProvider, type);
    }
}

var settings = new RefitSettings { UrlParameterFormatter = new Iso8601UrlParameterFormatter() };
var api = RestService.For<IMyApi>("https://api.example.com", settings);

DefaultUrlParameterFormatter already round-trips IFormattable values with the Format you pass via [Query(Format=...)], so overriding the formatter lets you apply "o" everywhere without annotating each parameter.