Automapper: mapping properties outside source entity - entity-framework

Question

I have a legacy ASP.NET Web forms application which uses ASP.NET GridView.
There's [User] class, which represents an entity from EF model, and then there's [UserDto]. All properties in the UserDto maps to the User class, except for one - which is RowCount. This is actually not a property related to the user itself, but in a legacy implementation, we have the total rowcount attached to each User object in the User list to show the correct page number in the Gridview.
So here's how my mapping goes:
config.CreateMap<User, UserDto>()
.ForMember(dest => dest.Id, opt => opt.MapFrom(u => u.UserId))
.ForMember(dest => dest.Username, opt => opt.MapFrom(u => u.UserName))
.ForMember(dest => dest.Usercode, opt => opt.MapFrom(u => u.UserCode))
.ForMember(dest => dest.FirstName, opt => opt.MapFrom(u => u.FirstName))
.ForMember(dest => dest.LastName, opt => opt.MapFrom(u => u.LastName))
.ForMember(dest => dest.Branch, opt => opt.MapFrom(u => u.Branch))
.ForMember(dest => dest.Groups, opt => opt.MapFrom(u => u.UserGroups))
.ForMember(dest => dest.AssignedUsers, opt => opt.MapFrom(u => u.User12.Select(s => s.FirstName + " " + s.LastName)));
Then I retrieve the users and map it to the DTO as follows:
var users = (from u in context.Users.Include("Branch")
where (u.FkBranchId == branchId || branchId == -1)
select u).ToList();
// get the total row count to support paging
var rowCount = users.Count;
var orderedList = CustomSort.GetSortedList(users, sortInfo.SortColumn, sortInfo.SortDirection).Skip(pageInfo.Skip).Take(pageInfo.PageSize).ToList();
return mapper.Map<List<EFModel.ClientData.User>, List<UserDto>>(orderedList);
Here I'm thrown an error, obviously, because the RowCount property in my DTO is not mapped. Notice that I want to map it to a property outside of the user object, i.e. the list count.
How do I do this?