c# - Get DateTime as UTC with Dapper

Question

I'm using Dapper to map my entities to SQL Server CE. If I save a DateTime with Kind=Utc, when I read it back I get a DateTime with Kind=Unspecified, which leads to all kind of problems.

Example:

var f = new Foo { Id = 42, ModificationDate = DateTime.UtcNow };
Console.WriteLine("{0} ({1})", f.ModificationDate, f.ModificationDate.Kind);
connection.Execute("insert into Foo(Id, ModificationDate) values(@Id, @ModificationDate)", f);
var f2 = connection.Query<Foo>("select * from Foo where Id = @Id", f).Single();
Console.WriteLine("{0} ({1})", f2.ModificationDate, f2.ModificationDate.Kind);

This code gives the following output:

20/09/2012 10:04:16 (Utc)
20/09/2012 10:04:16 (Unspecified)

I know I should be using a DateTimeOffset, but unfortunately SQL CE has no support for this type.

Is there a workaround? Can I tell Dapper to assume that all dates have DateTimeKind.Utc? And more generally, what are my options to customize the mapping?

---

EDIT: My current workaround is to patch the dates after Dapper has materialized the result, but it kind of smells...

var results = _connection.Query<Foo>(sql, param).Select(PatchDate);

...

static Foo PatchDate(Foo f)
{
    if (f.ModificationDate.Kind == DateTimeKind.Unspecified)
        f.ModificationDate = DateTime.SpecifyKind(f.ModificationDate, DateTimeKind.Utc);
    return f;
}

Answer 1

Adding this answer for anyone else who comes looking for a simple fix. This is possible now with the addition of SqlMapper.TypeHandler in Dapper.

Add this class to convert the value from the db to a datetime with the kind specified as UTC.

public class DateTimeHandler : SqlMapper.TypeHandler<DateTime>
{
    public override void SetValue(IDbDataParameter parameter, DateTime value)
    {
        parameter.Value = value;
    }

    public override DateTime Parse(object value)
    {
        return DateTime.SpecifyKind((DateTime)value, DateTimeKind.Utc);
    }
}

Then in my Global.asax file of my Web API I add the type handler to dapper.

SqlMapper.AddTypeHandler(new DateTimeHandler());

If you need to ensure you are always inserting dates as UTC, then on the SetValue method you can use:

parameter.Value = DateTime.SpecifyKind(value, DateTimeKind.Utc);