This sample snippet shows you how could you use Except predicate in EF.
The below code gets list of Customers except from cutomers orders not shipped in China. This works similiar to Not clauase or <> operator in T-SQL
public void ExceptEF()
var query = context.Customers.Select(e => e)
.Except(context.Orders.Where(o => o.ShipCountry == "China").Select(o => o.Customer));