# DateOnly in your .NET 6 API

**Date:** 2022-08-09  
**Author:** Kees C. Bakker  
**Categories:** .NET / C#  
**Original:** https://keestalkstech.com/dateonly-in-your-net-6-api/

![DateOnly in your .NET 6 API](https://keestalkstech.com/wp-content/uploads/2022/08/estee-janssens-zni0zgb3bkQ-unsplash.jpg)

---

Let's face it: sometimes `DateTime` is just too much: you only want to deal with dates. Since .NET 6, we finally have support for `DateOnly`. In this blog I'll look at how to interact with it and how to add it to your Swagger API docs.

## To and From DateTime

It is nice that we have a `DateOnly`, but there are plenty of occasions you'll need that good ol `DateTime` back. Converting them back and forth is easy:

```cs
// let's convert DateTime to DateOnly
var day = DateOnly.FromDateTime(DateTime.Now);

// let's convert DateOnly to DateTime
var dt = day.ToDateTime(new TimeOnly());
```

## Time travel with DateOnly

I need to work with months, so I'm interested in getting the first and the last date of the month. The following code was airlifted and adjusted from [StackOverflow](https://stackoverflow.com/a/31538863/201482):

```cs
public static class TimeTravelExtensions
{
    public static DateOnly FirstDayOfMonth(this DateOnly value) => new DateOnly(value.Year, value.Month, 1);

    public static int DaysInMonth(this DateOnly value) => DateTime.DaysInMonth(value.Year, value.Month);

    public static DateOnly LastDayOfMonth(this DateOnly value) => new DateOnly(value.Year, value.Month, value.DaysInMonth());

    public static DateOnly FirstDayOfWeek(this DateOnly value) => value.AddDays(-(int)value.DayOfWeek);
}
```

## DateOnly Web API support

The Web API doesn't have great support out of the box. I just want to use `DateOnly` like any other data structure (a string will do). Also, I would like [Swagger](https://github.com/domaindrivendev/Swashbuckle.AspNetCore) (openapi) to understand it. Fortunately, there are packages that will give you great support:

```shell
dotnet add package DateOnlyTimeOnly.AspNet --version 1.0.3
dotnet add package DateOnlyTimeOnly.AspNet.Swashbuckle --version 1.0.3
```

Add it to your dependency injection:

```cs
services
    .AddControllers(options => options.UseDateOnlyTimeOnlyStringConverters())
    .AddJsonOptions(options => options.UseDateOnlyTimeOnlyStringConverters());
```

Add it to Swagger:

```cs
services.AddSwaggerGen(options =>
{
    options.UseDateOnlyTimeOnlyStringConverters();
});
```

According to the [docs](https://github.com/maxkoshevoi/DateOnlyTimeOnly.AspNet#dateonlytimeonlyaspnet), this will add "support for receiving and returning DateOnly/TimeOnly as [ISO 8601 string](https://www.wikiwand.com/en/ISO_8601) to ASP.NET API". It will look something like this:

![A screenshot of a Swagger/Open API interface, showing how to work with DateOnly when using DateOnlyTimeOnly.AspNet.Swashbuckle.](https://keestalkstech.com/wp-content/uploads/2022/06/image-1.png)
*The input value is DateOnly and is shown with type string($date). The output day is shown in the ISO 8601 format.*