[BUG] LiteDB loses precision in DateTime

Version LiteDB 5.0.8 .NET Framework 4.8 / .NET Standard 2.0

Describe the bug LiteDB loses precision when serializes DateTime.

Code to Reproduce

class Foo
{
	public DateTime Value { get;set; }
}
...
var db = new LiteDatabase(@"C:\Temp\database.db")) { UtcDate = true };
var col = db.GetCollection<Foo>();
var expected = new Foo() { Value = new DateTime(637310234309996491) };
col.Insert(expected);
var actual = col.FindAll().First();
Console.WriteLine(actual.Value == expected.Value); // false
Console.WriteLine(actual.Value.Ticks) // 637310234309990000 instead of 637310234309996491

Expected behavior DateTime is the same after serialization/deserialization to the database

Screenshots/Stacktrace If applicable, add screenshots/stacktrace

Additional context A similar issue was reported a while ago: https://github.com/mbdavid/LiteDB/issues/420

[dropsonic]

Thanks!

If anyone is curious, I used the following code to make it work on 5.0.9:

var mapper = new BsonMapper();
mapper.RegisterType<DateTime>(
    value => value.ToString("o", CultureInfo.InvariantCulture),
    bson => DateTime.ParseExact(bson, "o", CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind));
mapper.RegisterType<DateTimeOffset>(
    value => value.ToString("o", CultureInfo.InvariantCulture),
    bson => DateTimeOffset.ParseExact(bson, "o", CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind));

using (var db = new LiteDatabase("instance.db", mapper))
{
    ...
}

[henon]

I agree with @dropsonic, this is a massive pitfall which everyone who stores and compares loaded DateTimes will encounter.

How about keeping the current format how it is for backwards compatibility for DateTime values saved until now but save all future values without precision loss and denote the newly saved values accordingly so that they are not interpreted as old DateTime values?

Also, I don’t understand, why does LiteDB have to follow the BSON spec in every detail even if it is to the user’s disadvantage? Couldn’t it handle DateTimes better and just document that deviation from the BSON spec, to all user’s advantage?