Question

Unfortunaltly I am maintaining a system that didnt take consideration into what will happen once the system has millions of records.

The issue I am having is the way the code is currently written mainly the GetList method actually returns every record from the database and the filtering is done at the getfull method.

I tryed changing this by passing the id of the adjustment to the getlist method however when i try to do .Where(a=>a.Id == journalid)
i get this error

Cannot implicitly convert type ‘System.Linq.IQueryable to ‘System.Data.Objects.ObjectQuery

public Adjustment GetFull(int id) {
            var result = GetList(id).FirstOrDefault(ja => ja.Id == id);
            if(result == null) {
                throw new InvalidOperationException(
                    String.Format(" Adjustment with Id={0} not found.", id)
                );
            }
            return LoadFullActivities(result);
        }


        private IQueryable<Adjustment> GetList(int journalid) {
            return GetList(journalid,"Original", "Activities",
                "Original.Employee", "Original.Employee.EmployeeType", 
                "Original.Employee.WorkType", "Original.Employee.Department", 
                "Original.Activities", "Original.Status", 
                "Original.Approver", "Status");
        }

        private IQueryable<Adjustment> GetList(int journalid, params string[] includes) {
            var tempResult = dataContext.AdjustmentSet;
            foreach (var property in includes) {
                tempResult = tempResult.Include(property).Where(a=>a.Id == journalid) ;
            }
            return tempResult;
        }

Answer 1

This would fix the error

private IQueryable<Adjustment> GetList(int journalid, params string[] includes) {
         var tempResult = dataContext.AdjustmentSet.AsQueryable();
         foreach (var property in includes) {
              tempResult = ((ObjectQuery<Adjustment>)tempResult).Include(property);
         }            
         return tempResult.Where(a=>a.Id == journalid);
      }

Those Includes slow down the query. Since the query is going to get only one row (and do other joins because of the includes) I don’t think the performance is so slow. To increase the performance add indexes for each foreign key. I guess a.Id has already a clustered index.