TryUpdateModel showing the curect data but db is not saving it - sql-server

Question

I'm trying to save a single item into a SQL Server tableusing TryUpdateModel. When debugging, I can see the value that needs to be updated, but the db.SaveChanges() call is not saving it.
My code:
[HttpGet]
public PartialViewResult _SubmitRev(int? id)
{
return PartialView();
}
[HttpPost]
public PartialViewResult _SubmitRev(int? id, WriterSubjectReviewVm model)
{
var loggedInUserId = User.Identity.GetUserId();
var member = db.Members.SingleOrDefault(m => m.ApplicationUserId == loggedInUserId);
var MySubjectDetails = (from c in db.subjects.Where(s => s.SubjectId == id) select c).AsNoTracking().Single();
model.rev.SubjectId = (int)id;
model.sub.SubjectId = MySubjectDetails.SubjectId;
var bad = MySubjectDetails.Bad;
model.sub.Bad = bad;
if (model.rev.GBU == "Bad")
{
int iBadRating = Convert.ToInt32(bad);
iBadRating++;
model.sub.Bad = iBadRating;
}
if (ModelState.IsValid)
{
// TryUpdateModel(model.sub, "Subject");
TryUpdateModel(model.sub);
db.SaveChanges();
return PartialView();
}
return PartialView(model);
}

Answer 1

Looking at your code, I would say that you aren't re-attaching your model back to the context. Let's break it down:
First, your model is coming into the method as a new object:
public PartialViewResult _SubmitRev(int? id, WriterSubjectReviewVm model)
Then you modify it a bit using data from your DB:
var MySubjectDetails = (from c in db.subjects.Where(s => s.SubjectId == id) select c).AsNoTracking().Single();
model.rev.SubjectId = (int)id;
model.sub.SubjectId = MySubjectDetails.SubjectId;
Important to note that you are pulling MySubjectDetails using .AsNoTracking(), which pulls it disconnected from the context, so this won't automatically save at all unless you re-attach it.
You then assign that disconnected entity to your model:
var bad = MySubjectDetails.Bad;
model.sub.Bad = bad;
Then you modify some more properties, then you check if the model is valid and try and save it:
if (ModelState.IsValid)
{
// TryUpdateModel(model.sub, "Subject");
TryUpdateModel(model.sub);
db.SaveChanges();
return PartialView();
}
At no point have you reconnected your model object back to the context (db), so when you call .SaveChanges(), what are you saving?
The Solution
At some stage you need to map the properties as posted to your Action (in the form of the WriterSubjectReviewVm view model) back onto a data model. Otherwise if that view model is actually a data model (and exists on your DB context in a collection somewhere) then you need to reattach it:
db.WriterSubjectReviews.Attach(model)
Or something similar - then when you call SaveChanges() it will actually save.