ASP.NET MVC 3 One-To-Many Can't Update Bridge Table - asp.net-mvc-3

Question

I've looked around for hours, but I can't seem to find a straight forward method for solving my problem.
Basically, I have a 1-to-many relationship, bridged with a table. My controller seems to handle the 'create' method perfectly, creating records within the '1' table and the bridging 'many' table.
However, the 'edit' method doesn't seem to modify/update the bridging table at all. Any thoughts on what I'm doing wrong, and why it differs from the 'create' approach?
For brevity, let's say I have the following model:
public class Incident
{
[Key]
public int IncidentID { get; set; }
public string Title { get; set; }
public virtual ICollection<IncidentResources> Resources{ get; set; }
}
And an Resource model:
public class Resource
{
[Key]
public int ResourceID{ get; set; }
public int Name { get; set; }
...OTHER FIELDS REMOVED FOR BREVITY...
}
And I am bridging these two via a bridging table and model:
public class IncidentResource
{
[Key]
public int IncidentResourceID { get; set; }
public int IncidentID { get; set; }
public int ResourceID { get; set; }
public virtual <Resource> Resource { get; set; }
}
In my Controllers, I have the following code:
[HttpPost]
public ActionResult Create(Incident incident)
{
//incident.Resources is returned as a valid object...
if (ModelState.IsValid)
{
db.Incidents.Add(incident);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(incident);
}
The above works perfectly! As I mentioned, the new Incident is inserted into the proper table, and all Resources assigned to the incident are added to the IncidentResources table.
However, the following code DOES NOT work this way for the edit...
[HttpPost]
public ActionResult Edit(Incident incident)
{
if (ModelState.IsValid)
{
//THE USER CAN ADD ADDITIONAL RESOURCES
foreach (IncidentResource r in incident.Resources)
{
r.IncidentID = incident.IncidentID;
}
db.Entry(incident).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(incident);
}
Again, the above seemingly does nothing to the IncidentResources table. Records are not added, removed, or updated. I don't receive an error either. It just doesn't do anything.
Please note that I DO NOT want to just trash the bridge table data and reinsert. I will have 1-to-many relationships to that data that I do not want to orphan.
What am I not understanding about how this works?

Answer 1

You need to attach the entity instance created outside EF and let EF know that it has been modified.
Try add:
db.Incidents.Attach(incident);
before you changing state. In your case your last block of code should looks like:
[HttpPost]
public ActionResult Edit(Incident incident)
{
if (ModelState.IsValid)
{
//THE USER CAN ADD ADDITIONAL RESOURCES
foreach (IncidentResource r in incident.Resources)
{
r.IncidentID = incident.IncidentID;
}
db.Incidents.Attach(incident);
db.Entry(incident).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(incident);
}

Answer 2

It seems the IncidentID in the IncidentResource object is not mapping as a Foreign Key to the Incident table. Try adding a ForeignKey annotation to explicitly set IncidentID as a Foreign Key pointing to Incident:
[ForeignKey("Incident")]
public int IncidentID { get; set; }

Answer 3

I wonder if, in your current code, Entity Framework is seeing that the Incident object hasn't been changed at all, and isn't trying to see if there are IncidentResources that need to be adjusted.
Try adding the following line in your loop:
db.Entry(r).State = EntityState.Modified;
EDIT: I should add that, after writing this answer, I was watching a talk by Julie Lerman on Entity Framework where she did mention that the "modified state won't cascade through a graph", which means that the above code should do it for you.

Answer 4

Unless you are tracking the IncidentID in a hidden field in the form, I would bet the problem stems from it trying to update a Incident that doesn't exist (IncidentID:0)
This will depend on your routes, but assuming the default route pattern:
[HttpPost]
public ActionResult Edit(int id, Incident incident)
{
incident.IncidentID = id;
if (ModelState.IsValid)
{
//THE USER CAN ADD ADDITIONAL RESOURCES
foreach (IncidentResource r in incident.Resources)
{
r.IncidentID = incident.IncidentID;
}
db.Entry(incident).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
return View(incident);
}

Answer 5

If you are able, you may try adding the foreign key IncidentID of the IncidentResource table to the primary key to make a composite primary key. I was having a similar issue and this was what helped me.
I got the solution from a couple other stackoverflow questions. My set up did not match these exactly because I am using AutoMapper with Entity model first unit of work approach but making the composite key on the relationship table fixed my problems.
Is it possible to remove child from collection and resolve issues on SaveChanges?
What's the difference between identifying and non-identifying relationships?

Answer 6

Shouldn't you be doing the following
[HttpPost]
public ActionResult Edit(Incident incident)
{
if (ModelState.IsValid)
{
//THE USER CAN ADD ADDITIONAL RESOURCES
foreach (IncidentResource r in incident.Resources)
{
r.IncidentID = incident.IncidentID;
db.Entry(r).State = EntityState.Modified;
}
db.SaveChanges();
return RedirectToAction("Index");
}
return View(incident);
}