Flutter wrong utc time from SQL Server database - sql-server

Question

I've got a problem with flutter recognizing my DateTime as UTC time. Via http request, I am storing some data inside my SQL Server database which contains a UTC DateTime. This is done via Entity Framework.
var workingTime = new WorkingTime()
{
StartDateTime = dto.StartDateTime.ToUniversalTime(),
EndDateTime = dto.EndDateTime.ToUniversalTime(),
...
};
await _repository.AddAsync(workingTime);
This looks quiet okay, the request was done at 2020-06-13 01-59-41:690 in Germany, so the stored data is the correct UTC time.
Now I am loading these data in my flutter app and if I debug my app, the loaded datetime says, that it is not a UTC time.
I am not sure, if I store the data wrong, or if I the parsing inside flutter is wrong, but I can't see me doing something wrong here.
Please tell me if you need code or more information.
Edit
So after a lot of testing, I found out something:
Debug.WriteLine(model.EndDateTime.Kind);
This prints "Unspecified". It seems like there is something wrong either in storing the DateTime or in reading from it.

Answer 1

Be explicit about the UTC every time. Indicate to the compiler you want the UTC time.
To get millisecondsSinceEpoch in UTC time:
DateTime dateTime=DateTime.now().toUtc();
int epochTime = dateTime.toUtc().millisecondsSinceEpoch;
To get Datetime in UTC:
DateTime dt=DateTime.fromMillisecondsSinceEpoch(millisecondsSinceEpoch).toUtc();

Answer 2

Store time as int in database. Milliseconds since epoch time.
DateTime dateTime=DateTime.now().toUtc();
int epochTime = dateTime.toUtc().millisecondsSinceEpoch;

Answer 3

After a lot of thinking I came along a good method for my case. I ended up implementing an extension method, that converts the Kind of every DateTime stored inside the Database to the UTC Kind when loaded.
Inside the DataContext:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// Convert all DateTimes to UTC
modelBuilder.TreatDateTimeAsUtc();
}
The extension method
public static class ModelBuilderExtensions
{
public static void TreatDateTimeAsUtc(this ModelBuilder modelBuilder)
{
var dateTimeConverter = new ValueConverter<DateTime, DateTime>(
v => v.ToUniversalTime(),
v => DateTime.SpecifyKind(v, DateTimeKind.Utc));
var nullableDateTimeConverter = new ValueConverter<DateTime?, DateTime?>(
v => v.HasValue ? v.Value.ToUniversalTime() : v,
v => v.HasValue ? DateTime.SpecifyKind(v.Value, DateTimeKind.Utc) : v);
foreach (var entityType in modelBuilder.Model.GetEntityTypes())
{
foreach (var property in entityType.GetProperties())
{
if (property.ClrType == typeof(DateTime))
{
property.SetValueConverter(dateTimeConverter);
}
else if (property.ClrType == typeof(DateTime?))
{
property.SetValueConverter(nullableDateTimeConverter);
}
}
}
}
}