Entity Framework overwrites data when 2 two people save data simultaneously - entity-framework

Question

In a function I pass a list of related values and loop over them to save changes in the database. All works well until 2 or more people use the same page to update different entities .Then only that data gets saved for which the changes were made more recently.
public bool UpdatePermanentDifferenceBL(List<PermanentDifferenceProperties> permDiffDetails)
{
try
{
int permanentDifferenceID=0;
int taxEntityID = 0;
int mapid = 0;
//using (TransactionScope scope = new TransactionScope(TransactionScopeOption.Required))
//{
Topaz.DAL.PermanentDifference permDiff;
for (int i = 0; i < permDiffDetails.Count; i++)
{
if ((bool)(HttpContext.Current.Session[GlobalConstant.currentDataSet]) == true && (int)(HttpContext.Current.Session[GlobalConstant.snapShotID]) == 0)
{
using (var ctx = new TopazDbContainer())
{
try
{
permanentDifferenceID = permDiffDetails[i].PermanentDifferenceID;
taxEntityID = permDiffDetails[i].TaxEntityID;
mapid = permDiffDetails[i].MapID;
permDiff = new Topaz.DAL.PermanentDifference();
permDiff = ctx.PermanentDifference.Where(p => p.PermanentDifferenceID == permanentDifferenceID && p.TaxEntityID == taxEntityID && p.MapID == mapid).SingleOrDefault();
permDiff.Business = permDiffDetails[i].Business;
permDiff.Interest = permDiffDetails[i].Interest;
permDiff.Corporate = permDiffDetails[i].Corporate;
permDiff.UnallocatedTax = permDiffDetails[i].UnallocatedTax;
permDiff.Total = permDiffDetails[i].Total;
permDiff.ModifiedBy = permDiffDetails[i].ModifiedBy;
permDiff.ModifiedDate = DateTime.Now;
ctx.SaveChanges();
}
catch (System.Data.OptimisticConcurrencyException ex)
{
permanentDifferenceID = permDiffDetails[i].PermanentDifferenceID;
taxEntityID = permDiffDetails[i].TaxEntityID;
mapid = permDiffDetails[i].MapID;
permDiff = new Topaz.DAL.PermanentDifference();
ctx.Refresh(System.Data.Objects.RefreshMode.StoreWins, permDiff);
permDiff = ctx.PermanentDifference.Where(p => p.PermanentDifferenceID == permanentDifferenceID && p.TaxEntityID == taxEntityID && p.MapID == mapid).SingleOrDefault();
permDiff.Business = permDiffDetails[i].Business;
permDiff.Interest = permDiffDetails[i].Interest;
permDiff.Corporate = permDiffDetails[i].Corporate;
permDiff.UnallocatedTax = permDiffDetails[i].UnallocatedTax;
permDiff.Total = permDiffDetails[i].Total;
permDiff.ModifiedBy = permDiffDetails[i].ModifiedBy;
permDiff.ModifiedDate = DateTime.Now;
ctx.SaveChanges();
}
}
}
//ctx.ContextOptions.UseLegacyPreserveChangesBehavior = true;
}
//}
//using (UnitOfWork uow = new UnitOfWork())
//{
// for (int i = 0; i < permDiffDetails.Count; i++)
// {
// if ((bool)(HttpContext.Current.Session[GlobalConstant.currentDataSet]) == true && (int)(HttpContext.Current.Session[GlobalConstant.snapShotID]) == 0)
// {
// Repository.PermanentDifferenceRepository pDiffRepo = new Repository.PermanentDifferenceRepository(uow);
// Topaz.DAL.PermanentDifference permDiff = pDiffRepo.GetByEntityId(permDiffDetails[i].PermanentDifferenceID, permDiffDetails[i].TaxEntityID, permDiffDetails[i].MapID);
// permDiff.Business = permDiffDetails[i].Business;
// permDiff.Interest = permDiffDetails[i].Interest;
// permDiff.Corporate = permDiffDetails[i].Corporate;
// permDiff.UnallocatedTax = permDiffDetails[i].UnallocatedTax;
// permDiff.Total = permDiffDetails[i].Total;
// permDiff.ModifiedBy = permDiffDetails[i].ModifiedBy;
// permDiff.ModifiedDate = DateTime.Now;
// pDiffRepo.ApplyChanges(permDiff);
// }
// else
// {
// int snapshotID = (int)(HttpContext.Current.Session[GlobalConstant.snapShotID]);
// SnapShotPermanentDifferenceRepository pDiffRepo = new SnapShotPermanentDifferenceRepository(uow);
// SnapShotPermanentDifference permDiff = pDiffRepo.GetByEntityId(permDiffDetails[i].PermanentDifferenceID, permDiffDetails[i].TaxEntityID, permDiffDetails[i].MapID,snapshotID);
// permDiff.SnapshotID = snapshotID;
// permDiff.Business = permDiffDetails[i].Business;
// permDiff.Interest = permDiffDetails[i].Interest;
// permDiff.Corporate = permDiffDetails[i].Corporate;
// permDiff.UnallocatedTax = permDiffDetails[i].UnallocatedTax;
// permDiff.Total = permDiffDetails[i].Total;
// permDiff.ModifiedBy = permDiffDetails[i].ModifiedBy;
// permDiff.ModifiedDate = DateTime.Now;
// pDiffRepo.ApplyChanges(permDiff);
// }
// }
// uow.SaveChanges();
return true;
}
catch (Exception ex)
{
TopazErrorLogs.AddTopazErrorLogBL(ex, 1, 1);
throw new TopazCustomException(GlobalConstant.errorMessage);
}
}
Any urgent assistance is much appreciated.

Answer 1

The common way to solve this is adding additional column to every table where you want to handle concurrency. This column will have ROWVERSION or TIMESTAMP data type. Once you map tables in EDMX you will get a new computed property of type byte[] and set its Concurrency mode to fixed. This setting will force EF to add additional WHERE condition to every UPDATE or DELETE statement validating that row version is the same as it was when the record was loaded from the database. If the row version is not the same (another thread updated the record) the record from modification is not found and you will get exception.
Database will change the value every time you update the record automatically. You just need to ensure that your entity uses the value which was retrieved when the entity was loaded from the database.

Answer 2

Apologies all the viewstate and to some extent session was the culprit and not EntityFramework.