Dec 22, 20211 min read

Converting DateOnly and TimeOnly to DateTime and vice versa in .NET 6

How DateOnly and TimeOnly can be used with legacy application where DateTime is already used?

How can we migrate to use this ?

How do we interact with external interface which are still using DateTime ?

Don’t worry .NET developers already thought of it and they have provided the proper methods to do the conversion.

Let’s look at the example.

Converting DateTime to DateOnly

// Creating DateTime object

DateTime testDateTime = new DateTime(2021,09,21);
// Creating DateOnly object from DateTime.

DateOnly testDateOnly = DateOnly.FromDateTime(testDateTime);
Console.WriteLine(testDateOnly.ToString());

//Output -> 09/21/2021

Converting DateTime to TimeOnly

// Creating DateTime object
DateTime testDateTime = new DateTime(2021,09,21,03,13,22);
// Creating TimeOnly object from DateTime.
TimeOnly testTimeOnly = TimeOnly.FromDateTime(testDateTime);
Console.WriteLine(testTimeOnly.ToLongTimeString());

//Output -> 03:13:22

Converting DateOnly to DateTime

// Creating DateOnly instance
DateOnly dateOnly = new DateOnly(2021, 9, 16);
// Converting DateOnly to DateTime by providing Time Info
DateTime 
testDateTime = dateOnly.ToDateTime(TimeOnly.Parse("10:00 PM"));
Console.WriteLine(testDateTime);

//Output -> 09/16/2021 22:00:00

As you can see, to convert from DateOnly to DateTime, we need to provide TimeOnly info along with it.

we can provide actual time or we can provide TimeOnly.MinValue to specify the midnight where time is not “relevant”.

Converting TimeOnly to DateTime

This is little tricky, if you think there are no scenario where you would be converting TimeOnly to DateTime, even if you have to then it would be same as we already did above in Converting DateOnly to DateTime section.

But it support to convert the TimeOnly to TimeSpan.

Let’s look at the example.

Converting TimeOnly to TimeSpan

//Creating TimeOnly instance
TimeOnly timeOnly = TimeOnly.Parse("10:00 PM");
// Converting TimeOnly to TimeSpan

TimeSpan timeSpan = timeOnly.ToTimeSpan();
Console.WriteLine(timeSpan);

//Output -> 22:00:00