AutoMapper Two-way mapping

gistfile1.cs

Mapper.CreateMap<Design, DesignSubmitViewModel>()
    .ForMember(d => d.Tags, opt => opt.MapFrom(d => d.Tags.Aggregate("", (total, tag) => total + (tag.Name + ", ")).Trim(' ',',')));

Mapper.CreateMap<DesignSubmitViewModel, Design>()
    .ForMember(d => d.Competition, opt => opt.Ignore())
    .ForMember(d => d.Tags, opt => opt.MapFrom(d => d.Tags.Split(',').Select(name => new Tag() { Name = name.Trim() })));