dealing with datetime and time zone in .net 7 razor page app in multi country usage-CodePudding

I'm programming a web application that clients can make appointments and choose a time: e.g: the admin has set the appointment times from 8 AM till 8 PM based on his own timezone (users timezoneId are saved in the database ) admin timezone: 3:30 There is 05:30 time difference between this client and admin . a client visits the site and tries to make an appointment for tomorrow from 10 AM to 10:30 AM. the client wants 10 AM based on his/her own timezone if we compute it based on the admin timezone 10 AM would be 3:30PM till 4:00 PM

what datatype I have to use for saving time in DB (SQL server) DateTime or datetimeoffset?
is there any implementation service for converting from another time zone to another? ( i have used timezoneinfo and DateTime convert built-in methods but all of them had problems)
is daylight saving an important thing? when I use convert methods (TimeZoneInfo.ConvertTimeFromUtc())it considers daylight saving but when I use this method(TimeZoneInfo.ConvertTimeToUtc()) I think it doesn't consider daylight saving. I don't know that is my system design is correct or not isn't it better to save all times in the 00:00 timezone even with admin configs? I'm so confused can someone help me? I have tried DateTime and datetimeoffset built-in methods and also timezoneinfo built-in methods but I couldn't handle it

CodePudding user response：

datetimeoffset includes both date and time including the offset from the UTC. so you can store the specific time zone time.

NodaTime by sir Jon Skeet is a very good library to solve timezone-related problems, I have personally used it. you can also refer TimeZoneConverter library.

I personally prefer storing the UTC DateTime in the database and shows the time specific to the user's time zone in such scenarios.

Defnility Daylight Saving Time is a very important factor to be considered when working across different timezone.

you have to do testing around different timezones, DST cases. I have personally used the library Bogus for generating different times during my testing.

CodePudding user response：

Finally i solved my problem .
now i use datetime instead of datetimeoffset.
I use DateTime.UtcNow() method to save current time in save changes.
I save user TimezoneId in database
i wrote 2 extension methods for datetime converters :
`

public static DateTime ToUserTime(this DateTime targetTime, string timeZoneId)
{
    var timezone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
    return TimeZoneInfo.ConvertTimeFromUtc(targetTime, timezone);
}
public static DateTime ToUtc(this DateTime targetTime, string timeZoneId)
{
    var timezone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
    return TimeZoneInfo.ConvertTimeToUtc(targetTime, timezone);
}

Thanks to everyone who helped with this question