How can you update a Linq Expression with additional parameters?

Question

I have a Linq Expression, which may be altered depending on certain conditions. An example of what I would like to do (left blank the bit I am not sure about):

Answer 1

If you Get method retrives the data and returns in memory objects the you could do so

Expression> filter = (Project p) => p.UserName == "Bob";
if(showArchived) {
     filter = (Project p) => p.UserName == "Bob" && p.Archived;
}
IEnumerable projects = unitOfWork.ProjectRepository.Get(filter);

EDIT

Just to point out. When you use .ToList() method it enumerates the Queryable, i.e. makes a database request.