ulong is not be stored correctly in LiteDatabse

I am now making a MMO game using Unity. Also I am using the LiteDB to store users data. UserModel looks like this.

Everything is working correctly except for the mUserOwnerClientId. The variable type is ulong and I tried to store ulong.MaxValue. But the stored value was -1 and when I tried to read from database, there was an error because ulong could not be less than zero.

So I have a question here.

Does LiteDB support ulong storing?

LiteDB supports long by default, not ulong (unsigned).

But you can tell it how to handle the serialization and deserialization of a type it doesn't know with BsonMapper before using your database:

BsonMapper.Global.RegisterType<ulong>(
    unsignedLong => new BsonValue(unsignedLong.ToInt64WithSameBits()),
    bson => bson.AsInt64.ToUInt64WithSameBits()
);

/// <summary>
/// Extra methods for <see cref="ulong"/> type.
/// </summary>
public static class UInt64ExtensionMethods
{
    /// <summary>
    /// Takes the bits of the provided <see cref="ulong"/> value and returns them as a <see cref="long"/>, which might be a completely different number.
    /// </summary>
    /// <remarks>
    /// See https://stackoverflow.com/questions/13056230/copy-bits-from-ulong-to-long-in-c-sharp .
    /// </remarks>
    public static long ToInt64WithSameBits(this ulong value)
    {
        return unchecked((long) value);
    }
}

Then when you want to use queries you can use the BsonMapper again:

ulong playerID = 1234;
var query = Query.EQ(nameof(PlayerDocument.PlayerID), BsonMapper.Global.Serialize(playerID));