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Strange anomoly with: Attaching an entity of type 'X' failed because another entity of the same type already has the same primary key value

I had a similar issue with this question, when updating a record using EF6.
I really thought I had cracked the whole updating thing, but now have to almost identical functions updating in what I think was an identical way. One works, the other doesn't. I have fixed the one that doesn't work by using Jamie's comment in the above question, but I'd like to understand if the function that works, really shouldn't and so is on borrowed time and I should make more like the 'fixed' one. Or, why the 'fixed' one didn't work in the first place. I even moved them into the same controller so that the database (DB) context was guaranteed the same. Have I missed something and they are not identical (functionally) at all?
It might also help some others out there that struggle with this as I did.
The function that works (cut down) is:
[HttpPost]
[Route("UpdateAddBusinessService")]
public async Task<IHttpActionResult> UpdateAddBusinessService(BusinessServiceDTO servicetoupdateoradd)
{
... pre check stuff...
try
{
if (servicetoupdateoradd.Id != null) // This is an existing service to be updated - if Is Null then create new
{
BusinessService businessService = await db.BusinessServices.FindAsync(servicetoupdateoradd.Id);
if (businessService != null)
{
Mapper.Map(servicetoupdateoradd, businessService);
db.Entry(businessService).State = EntityState.Modified;
await db.SaveChangesAsync();
return Ok("Service Updated");
}
else
The function that doesn't work is:
[HttpPost]
[Route("UpdateImage")]
public async Task<IHttpActionResult> UpdateImage(ImageDTO imageDTO)
{
... pre check stuff ...
try
{
// First find the image
// Image imagetoupdate = await db.Images.FindAsync(imageDTO.Id); <<-This FAILS.
Image imagetoupdate = db.Images.AsNoTracking().Single(x => x.Id == imageDTO.Id); <<- This WORKS
if (imagetoupdate != null)
{
imagetoupdate = Mapper.Map<ImageDTO, Image>(imageDTO); // Move the stuff over..
db.Entry(imagetoupdate).State = EntityState.Modified;
await db.SaveChangesAsync();
return Ok();
}
I wondered (as you will no doubt), if my Mapper function was doing anything, but I suspect not (without digging too deep, but I guess it could be), my Mapper.Config functions for the two DTO's are very similar:
cfg.CreateMap<Image, ImageDTO>();
cfg.CreateMap<ImageDTO, Image>();
and:
cfg.CreateMap<BusinessService, BusinessServiceDTO>();
cfg.CreateMap<BusinessServiceDTO, BusinessService>();
I would really just like to understand the 'correct' way of doing this so it doesn't bite me again. Thanks in advance.
EDIT: I was asked (quite reasonably) if the 'pre-check stuff' does anything to fetch the data, it doesn't, but there is a subtle difference, that I might have missed...
This is from the BusinessService function that works:
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
string userid = User.Identity.GetUserId(); //Check user is valid
if (servicetoupdateoradd.UserId != userid)
{
var message = "User Id Not found - Contact support";
HttpResponseMessage err = new HttpResponseMessage() { StatusCode = HttpStatusCode.ExpectationFailed, ReasonPhrase = message };
return ResponseMessage(err);
}
This is from the UpdateImage function that didn't work:
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
string userid = User.Identity.GetUserId();
SGGUser user = db.Users.Find(userid); // Use this find and not UserManager becuase its a different context and buggers up the file save
if (user == null)
{
var message = "User Id Not found - Contact support";
HttpResponseMessage err = new HttpResponseMessage() { StatusCode = HttpStatusCode.ExpectationFailed, ReasonPhrase = message };
return ResponseMessage(err);
}
I see that in this one, though I don't fetch the relevant data, I do use the 'db' context.. could that be it?? The Image object does contain a reference to the user, so maybe that does some magic in the background code?
Appologies, I just didn't want to clutter up the question too much...

This line:
Mapper.Map(servicetoupdateoradd, businessService);
and this line:
imagetoupdate = Mapper.Map<ImageDTO, Image>(imageDTO); // Move the stuff over..
look similar, but do two different things.
The first line will tell Automapper to copy values from the first object over to the second object reference using the mapping rules.
The second line will tell Automapper to make a completely new reference to the entity with the mapped over values from the provided object and return it.
So in the first case, the entity reference is preserved to the one the DbContext knows about. The reference was loaded from a DbContext and should be tracking changes so you shouldn't even need to set it's entity state. In the second case, Automapper is creating an entirely new reference and assigning it over top the original reference. EF is treating that as a completely new instance and trying to attach it, resulting in it complaining because the context had already loaded that entity, you just overwrote the reference.
It should work if you change the second instance to:
Mapper.Map(imageDTO, imagetoupdate);

Controller method not updating(same result every time)

I have following method in my mvc controller:
[HttpGet]
public ActionResult UserProfile(String username)
{
var user = db.Users.Find(username);
return View(user);
}
This function returns View with user profile. But result of this is the same, regardless of changes in database.
When I debug it seems like db is not changing at all, while in other controllers everything works just fine.
EDIT:
Place when I make changes
public ActionResult ExecuteRetreive(String username, String ISBN)
{
if (IsValid(username))
{
var resBook = db.Books.Find(ISBN);
var resUser = db.Users.Find(username);
var resRentedBooks = (from rb in db.RentedBooks
join b in db.Books on rb.ISBN equals b.ISBN
where b.ISBN == ISBN
where rb.Login == username
where rb.Returned == null
select rb).FirstOrDefault();
if (resRentedBooks == null)
{
return RedirectToAction("Fail", "FailSuccess",
new { error = "" });
}
resRentedBooks.Returned = DateTime.Now;
resBook.IsRented = false;
resUser.RentedBooks--;
db.SaveChanges();
return RedirectToAction("Success", "FailSuccess");
}
else
{
return RedirectToAction("Fail", "FailSuccess",
new { error = "Niepoprawna nazwa użytkownika" });
}
}
Im new to this so dont laugh at my code :P When I display resUser.RentedBooks--; it is the same every time.

As a follow up to what #JeroenVannevel said in the comments, another problem that you might be having because you're using a static context (and one that I've had to deal with in the past) is that once a specific DbContext has loaded an entity (or a set of entities, in my case) it won't tend to refresh just because some outside changes were made in the database. It loads those entities into Local and just refers to those automatically if you query for it.
The solution, then, is to always put your DbContext calls wrapped up in a using block, since DbContext implements IDisposable.
One word of caution with this approach, since you're using MVC: If you are using lazy loading, and you know that your View will need some information from a child object (or to list the names of a collection of child objects), you will absolutely need to hydrate those child entities before you get out of the using block, or you will find yourself getting exceptions saying that your context has been disposed.

LINQ to SQL Field Won't Update (Sometimes)

I have a MVC Web Application using the following approach:
public class MyController : Controller
{
public FooRepository fooRepository = new FooRepository();
public BarRepository barRepository = new BarRepository();
public ActionResult UpdateItems(int id, int range1, int range2)
{
Foo foo = fooRepository.GetItem(id);
List<Bar> bars = barRepository.GetItemsByRange(range1, range2);
// Some validation rules here...
DoSomeWork(foo, bars);
// Show confirmation / error message
}
private void DoSomeWork(Foo foo, List<Bar> bars)
{
foreach(int i = 0; i < bars.Count; i++)
{
bars[i].Prop1 = foo.Prop1; // This field is updated
bars[i].Owner = "someuser"; // This one too
bars[i].Status = BarStatus.SomeStatus; // This isn't...
}
foo.Status = FooStatus.SomeStatus; // Ok
// Calls DataContext.SubmitChanges()
fooRepository.SubmitChanges();
barRepository.SubmitChanges();
}
}
However, in some "random" cases (I see no pattern), one of the fields doesn't get updated, as noted in the comments.
It seems like LINQ isn't recognizing the field's update, so it gets excluded from the generated query.
Can anyone tell me if I'm missing something here, what could be causing it and/or how can I solve it?
Note: I don't get any Exception and can't verify this case in a development scenario.

From my experience if the error is random and you can't reproduce in development than the problem is user error.
Programming would be really hard if the .net framework or the CLR just randomly decided to do things differently.

You probably have an implicit/explicit bind exclusion floating around somewhere
[Bind(Exclude="...,Status,...")]
Just guessing of course

If Linq thinks that the Status is already BarStatus.SomeStatus, then it won't update it.
What can happen is that you find a record with the status set to this value, and then some other routine changes it, and then, if you are using your same DataContext, you will get the old value from the cached copy and hence Linq thinks that it does not need to update it.

LINQ: SubmitChanges() not updating my record

Not to sound like a broken record here (there a few posts that look like this one) but none of them seem to solve my problem. It seems that when you want to update
private bool resetPassword(string password)
{
try
{
var db = new SchedulerDBDataContext();
// since this is a instance method, I grab the ID from _this_
AdminUser user = db.AdminUsers.SingleOrDefault(t => t.ID == _ID);
if (user != null)
{
// this method DOES update these two fields.
SchedUtil.md5Hash(password, ref user._EncryptedPassword, ref user._PasswordSalt);
// I threw these in there to try something... it didn't work.
//user._EncryptedPassword = user.EncryptedPassword;
//user._PasswordSalt = user.PasswordSalt;
// this DOESN'T do anything.
db.SubmitChanges();
return true;
}
return false;
}
catch (Exception)
{
return false;
}
}
Maybe this a dumb question but I'm retrieving this from the db... why not just update this's properties. I'm guess I need to pull it through the DBContext I guess.

You should be setting the public properties and not the private values.
// I threw these in there to try something... it didn't work.
//user._EncryptedPassword = user.EncryptedPassword;
//user._PasswordSalt = user.PasswordSalt;
This won't trigger any updates.
Even if you do :
user.EncryptedPassword = user._EncryptedPassword;
user.PasswordSalt = user._PasswordSalt;
this won't trigger any change either as you are not actually changing the values
You can do something like
string newEncryptedPassword;
string newPasswordSalt;
SchedUtil.md5Hash(password, ref newEncryptedPassword, ref newPasswordSalt);
user.EncryptedPassword = newEncryptedPassword;
user.PasswordSalt = newPasswordSalt;
Also check that your table has a primary key, otherwise Linq will not track the changes.

DJ,
Are you sure
user._EncryptedPassword ,
user._PasswordSalt
are the properties ? I think you LINQ TO SQL creates public and private properties.
Can you set them
user.EncryptedPassword ,
user.PasswordSalt
like this ?
Ved

To troubleshoot your code, try any of these suggestions:
while debugging the code, I'll assume that your object is not null.
ensure that your properties are actually changed. It's odd that you're using pipe-prefixed field names, but either way: while debugging, check that your properties actually have new values.
use SQL Server Profiler to capture the SQL statement sent to the database server. You'll then be able to re-run this UPDATE query back into SQL Management Studio, and determine how many records are effected. You'll also be able to see the values passed in the UPDATE statement.

Ved pointed out one possible problem. Just in case that doesn't work, you should double check your LINQ to SQL class' AdminUser class definition and make sure that the generated code implements the INotifyPropertyChanging and INotifyPropertyChanged interfaces. There are some cases where the designer will not implement these interfaces which prevents updates from working. e.g., not declaring a primary key.

LINQ to SQL: To Attach or Not To Attach

So I'm have a really hard time figuring out when I should be attaching to an object and when I shouldn't be attaching to an object. First thing's first, here is a small diagram of my (very simplified) object model.
In my DAL I create a new DataContext every time I do a data-related operation. Say, for instance, I want to save a new user. In my business layer I create a new user.
var user = new User();
user.FirstName = "Bob";
user.LastName = "Smith";
user.Username = "bob.smith";
user.Password = StringUtilities.EncodePassword("MyPassword123");
user.Organization = someOrganization; // Assume that someOrganization was loaded and it's data context has been garbage collected.
Now I want to go save this user.
var userRepository = new RepositoryFactory.GetRepository<UserRepository>();
userRepository.Save(user);
Neato! Here is my save logic:
public void Save(User user)
{
if (!DataContext.Users.Contains(user))
{
user.Id = Guid.NewGuid();
user.CreatedDate = DateTime.Now;
user.Disabled = false;
//DataContext.Organizations.Attach(user.Organization);
DataContext.Users.InsertOnSubmit(user);
}
else
{
DataContext.Users.Attach(user);
}
DataContext.SubmitChanges();
// Finished here as well.
user.Detach();
}
So, here we are. You'll notice that I comment out the bit where the DataContext attachs to the organization. If I attach to the organization I get the following exception:
NotSupportedException: An attempt has been made to Attach or Add an
entity that is not new, perhaps having
been loaded from another DataContext.
This is not supported.
Hmm, that doesn't work. Let me try it without attaching (i.e. comment out that line about attaching to the organization).
DuplicateKeyException: Cannot add an entity with a key that is already
in use.
WHAAAAT? I can only assume this is trying to insert a new organization which is obviously false.
So, what's the deal guys? What should I do? What is the proper approach? It seems like L2S makes this quite a bit harder than it should be...
EDIT: I just noticed that if I try to look at the pending change set (dataContext.GetChangeSet()) I get the same NotSupportedException I described earlier!! What the hell, L2S?!

It may not work exactly like this under the hood, but here's the way I conceptualize it: When you summon an object from a DataContext, one of the things Linq does is track the changes to this object over time so it knows what to save back if you submit changes. If you lose this original data context, the Linq object summoned from it doesn't have the history of what has changed in it from the time it was summoned from the DB.
For example:
DbDataContext db = new DbDataContext();
User u = db.Users.Single( u => u.Id == HARD_CODED_GUID );
u.FirstName = "Foo";
db.SubmitChanges();
In this case since the User object was summoned from the data context, it was tracking all the changes to "u" and knows how to submit those changes to the DB.
In your example, you had a User object that had been persisted somewhere (or passed from elsewhere and do not have it's original DataContext it was summoned from). In this case, you must attach it to the new data context.
User u; // User object passed in from somewhere else
DbDataContext db = new DbDataContext();
u.FirstName = "Foo";
DbDataContext.Users.Attach( u );
db.SubmitChanges();
Since the relationship between user and organization is just a GUID (OrganizationId) in your data model, you only have to attach the user object.
I'm not sure about your scaffolding code, but maybe something like this:
private const Guid DEFAULT_ORG = new Guid("3cbb9255-1083-4fc4-8449-27975cb478a5");
public void Save(User user)
{
if (!DataContext.Users.Contains(user))
{
user.Id = Guid.NewGuid();
user.CreatedDate = DateTime.Now;
user.Disabled = false;
user.OrganizationId = DEFAULT_ORG; // make the foreign key connection just
// via a GUID, not by assigning an
// Organization object
DataContext.Users.InsertOnSubmit(user);
}
else
{
DataContext.Users.Attach(user);
}
DataContext.SubmitChanges();
}

So "attach" is used when you take an object that exists from the database, detach it (say by marshalling it over a webservice somewhere else) and want to put it back into the database. Instead of calling .Attach(), call .InsertOnSubmit() instead. You're almost there conceptually, you're just using the wrong method to do what you want.

I used an big table with 400+ columns. No way am I going to map and test all that!
Get the original object from database, and attach it with the amended object. Just make sure the object coming back in is fully populated other wise it will override it the DB with blanks!
Or you can copy the original GET into memory and work on a proper copy (not just reference) of the MOdel, then pass the original and the changed one in, instead of re getting like I do in the example. This is just an example of how it works.
public void Save(User user)
{
if (!DataContext.Users.Contains(user))
{
user.Id = Guid.NewGuid();
user.CreatedDate = DateTime.Now;
user.Disabled = false;
user.OrganizationId = DEFAULT_ORG; // make the foreign key connection just
// via a GUID, not by assigning an
// Organization object
DataContext.Users.InsertOnSubmit(user);
}
else
{
var UserDB = DataContext.Users.FirstOrDefault(db => db.id == user.id); //Costs an extra call but its worth it if oyu have 400 columns!
DataContext.Users.Attach(user, userDB); //Just maps all the changes on the flu
}
DataContext.SubmitChanges();
}