Question

This section simply reads from an excel spreadsheet. This part works fine with no performance issues.

IEnumerable<ImportViewModel> so=data.Select(row=>new ImportViewModel{
                  PersonId=(row.Field<string>("person_id")),
                  ValidationResult = ""
                  }).ToList();

Before I pass to a View I want to set ValidationResult so I have this piece of code. If I comment this out the model is passed to the view quickly. When I use the foreach it will take over a minute. If I hardcode a value for item.PersonId then it runs quickly. I know I’m doing something wrong, just not sure where to start and what the best practice is that I should be following.

foreach (var item in so)
                {
                    if (db.Entity.Any(w => w.ID == item.PersonId))
                    {
                        item.ValidationResult = "Successful";
                    }
                    else
                    {
                        item.ValidationResult = "Error:  ";
                    }
                 } 

return View(so.ToList());

Answer 1

You need to do something like this :

var ids = so.Select(i=>i.PersonId).Distinct().ToList();
// Hitting Database just for this time to get all Users Ids
var usersIds = db.Entity.Where(u=>ids.Contains(u.ID)).Select(u=>u.ID).ToList();
foreach (var item in so)
                {
                    if (usersIds.Contains(item.PersonId))
                    {
                        item.ValidationResult = "Successful";
                    }
                    else
                    {
                        item.ValidationResult = "Error:  ";
                    }
                 } 

return View(so.ToList());