public class GiftLists
{
    [Column("gift_list_id")]
    public int Id { get; set; }

    [Required]
    [Column("name")]
    [MaxLength(50)]
    public string Name { get; set; }

    public string UserId { get; set; }
    public Users Users { get; set; }

    [Column("created_on")]
    public DateTime CreatedAt { get; set; }

    public List<GiftItem> GiftItems { get; set; }
}

public async Task<int> CreateList(GiftListDto glist)
    {
        // Check for user in table
        var user = await _unitOfWork.Users.GetUserByIdAsync(glist.UserId);
        if (user == null)
        {
            // Already in table
        }
        else
        {
            // If not in table, add it.
            _unitOfWork.Users.Add(new Users
            {
                UserId = glist.UserId
            });
        }

        //_unitOfWork.GiftLists.Add(new GiftLists
        //{
        //    Name = glist.Name,
        //    Users = new Users
        //    {
        //        UserId = glist.UserId
        //    }
        //});
        return await _unitOfWork.CompleteAsync();
    }

public class GiftListRepository : Repository<GiftLists>, IGiftListRepository
{
    public GiftListRepository(ApplicationDbContext context) : base(context)
    {
    }

    public override void Add(GiftLists glist)
    {
        // Check if user exists...
        /* If not; add new user via GiftList navigation property
           while also adding the GiftList entry */
    }
}