Entity framework tracking wrong model object after helper method - entity-framework

Question

Below is some basic code that's a part of our Create controller method. If a certain checkbox is selected, we want to create a copy of the agenttransmission object we are currently creating, with a couple fields altered.
When the program goes into the helper method, it creates the sub record without incident, however for some reason, when the program finishes and comes back to the Create method, the model object agenttransmission becomes the sub model object. All value, including the PK are suddenly pressent in the agenttransmission object.
Not sure how this is happening since there is a string return value on the helper method and no fields are touched on the agenttransmission record.
Create method
//Create substat if requested
if (agenttransmission.OverrideId)
{
status += ". " + CreateSubStat(agenttransmission);
}
Helper method
public string CreateSubStat(AgentTransmission master)
{
string msg = string.Empty;
if (ModelState.IsValid)
{
using (AgentResourcesEntities tempDb = new AgentResourcesEntities())
{
try
{
//Check to see if substat already exists
var check = (from a in db.AgentTransmission
where a.ParentId == master.ID && a.RecordStatus.Equals("P")
select a).ToList();
if (check.Count > 0) return string.Empty;
//If not add dependent record
AgentTransmission sub = master;
sub.OverrideId = false;
sub.DRMCompanyId = string.Empty;
sub.CONCode = "00";
sub.RecordStatus = "P";
sub.ParentId = master.ID;
sub.ID = 0;
sub.IsSubstat = true;
sub.SendToDynamicsOptions = "N";
sub.SendToNMF = false;
//Remove blanks from ClearinghousePartners list
sub.ClearinghousePartners.RemoveAll(
x =>
string.IsNullOrWhiteSpace(x.ClearingHouseName) &&
string.IsNullOrWhiteSpace(x.TradingPartnerName) && x.StartDate == null);
sub.AgentRelationshipCodes.RemoveAll(
x =>
string.IsNullOrWhiteSpace(x.RelationshipId) &&
!x.EffectiveDate.HasValue && x.Id == 0);
foreach (var item in sub.AgentRelationshipCodes)
{
item.LastChangeDate = DateTime.Now;
item.LastChangeId = SecurityRules.GetUserName(User);
item.AgentTransmission = sub;
item.AgtTableId = sub.ID;
}
foreach (var item in sub.ClearinghousePartners)
{
item.AgentTransmission = sub;
item.AgtTransId = sub.ID;
}
db.AgentTransmission.Add(sub);
db.SaveChanges();
msg = "Substat saved with status of 'Dependent'.";
}
catch (DbEntityValidationException dbEx)
{
msg = "Error creating substat. IT has been informed and will respond shortly.";
SendEmail.ErrorMail(dbEx.Message, SecurityRules.GetUserName(User));
}
catch (Exception ex)
{
msg = "Error creating substat. IT has been informed and will respond shortly.";
SendEmail.ErrorMail(ex, SecurityRules.GetUserName(User));
}
}
}
else
{
//Invalid ModelState error handling
string messages = string.Join("; ", ModelState.Values
.SelectMany(x => x.Errors)
.Select(x => x.ErrorMessage));
SendEmail.ErrorMail("Error Creating Substat: " + messages, SecurityRules.GetUserName(User));
msg = "Error creating substat. IT has been informed and will respond shortly.";
}
return msg;
}

Answer 1

The line...
AgentTransmission sub = master;
...doesn't copy master to sub, but assigns it to sub, because AgentTransmission is a reference type. So everything you do to sub you do to master.
You either must clone master to sub (create a new object and copy its properties), or re-fetch the master object from the database after the CreateSubStat call.