How can I configure LiteDb to accept DateTimeOffset as dictionary key?

Question

Given the following sample:

class Data
{ 
    public Dictionary<DateTimeOffset, string> Dict { get; set; }
    public ObjectId Id { get; set; }
}

void Main()
{
    var dbf = Path.GetTempFileName();
    
    try
    {
        using var db = new LiteDatabase(dbf);

        var datas = db.GetCollection<Data>();

        var data = new Data
        {
            Dict = new() { { DateTimeOffset.Now, "apple" }, {DateTimeOffset.Now.AddDays(1), "pear"} }
        };
        
        datas.Upsert(data);
        
        var got = datas.FindById(data.Id);
        
        got.Dump();
    }
    catch (Exception ex)
    {
        ex.Dump();
    }
    finally
    {
        File.Delete(dbf);
    }   
}

The data is persisted as expected, but I am getting Invalid cast from 'System.String' to 'System.DateTimeOffset'. when trying to retrieve the data.

Can I specify somehow the serializer for the key? I worked it around by storing the UNIX Epoch instead, but it is counterintuitive to work with it like that.

Answer 1

AFAIK, LiteDB uses BsonValue as internal storage format, and by default, it may not handle complex types like DateTimeOffset as keys in a dictionary.

So you can create a custom serializer for DateTimeOffset keys, and LiteDB allows you to register custom serializers using the BsonMapper.Global

For example:

BsonMapper.Global.RegisterType(
    serialize: key => key.ToString(), // Convert DateTimeOffset to string for serialization.
    deserialize: bson => DateTimeOffset.Parse(bson.AsString) // Parse string back to DateTimeOffset during deserialization.
);

By registering this custom serializer before interacting with LiteDB database, you can ensure that DateTimeOffset keys are properly serialized and deserialized.