Debugging Optimistic Concurrency with AJAX Call - asp.net

Question

I'm currently having a problem with optimistic concurrency in my ASP.NET MVC application.
Essentially, this following controller works fine when called upon once. However, I have a page that is made to modify residents in six different groups at the same time. This is where the problem occurs. Basically, I post up the list of residents one at a time for each list so there are essentially six concurrent ajax calls that hit the server at the same time. (This may be what I need to change, but I am not sure!)
The javascript ajax call posts up the id of the group along with a list of the resident IDs. The residents are then added to the groups references. I have been looking into refreshing the state, but this isn't working as it seems only one of the six groups is updated. I have tried also letting the client win. I really just need some guidance and tips on resolving this issue!
Here is my current code in my controller:
var group = _context.TherapyGroups.Include(r => r.Residents)
.Where(x => x.ID.ToString() == groupid).FirstOrDefault();
if(group == null)
{
throw new HttpResponseException(HttpStatusCode.NotFound);
}
group.Residents.Clear();
foreach(var id in residents)
{
var resident = _context.Residents.Where(x => x.ID.ToString() == id).FirstOrDefault();
if(resident == null)
{
throw new HttpResponseException(HttpStatusCode.NotFound);
}
group.Residents.Add(resident);
}
bool saveFailed;
do
{
saveFailed = false;
try
{
_context.SaveChanges();
}
catch (DbUpdateException e)
{
saveFailed = true;
((IObjectContextAdapter)_context).ObjectContext.Refresh(RefreshMode.StoreWins, _context.Residents);
}
} while (saveFailed);

Answer 1

Wasn't sure how to fix the issue you are having with the code you have, so tried simplifying it a bit. See if this helps:
var groupId = _context.TherapyGroups.FirstOrDefault(x => x.ID.ToString() == groupid).Select(x => x.ID);
if(groupId == "") // or if(groupId == 0), not sure type of x.ID
{
throw new HttpResponseException(HttpStatusCode.NotFound);
}
// Get all of the residents whose Id is in the residents list
var residentObjects = _context.Residents.Where(x => residents.Contains( x.ID.ToString()));
// Update the groupId for each resident
foreach(var resident in residentObjects)
{
resident.GroupId = groupId;
}
var saveFailed = false;
try
{
_context.SaveChanges();
}
catch (DbUpdateException e)
{
saveFailed = true;
}