Error attaching entity because of same primary key when trying to save an update

Question

I am trying to save an update to an existing database entry but when I do I get the error:

Attaching an entity of type 'FFInfo.DAL.Location' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate.

This is my controller's code. The save method I am using is the same I use in a few other areas to update data with no problems.

[HttpPost, ValidateAntiForgeryToken]
public ActionResult EditLocation(AddEditLocationVM model, HttpPostedFileBase MapFile)
{
    try
    {
        using (var db = new GeographyContext())
        {
            model.Sections = new SelectList(db.Sections.Where(s => s.ID > 1).OrderBy(s => s.Title), "ID", "Title").ToList();
            model.GeographyTypes = new SelectList(db.GeographyTypes.Where(gt => gt.SectionID == model.Section).OrderBy(gt => gt.Name), "ID", "Name").ToList();
            model.ParentLocations = new SelectList(db.Locations.Where(l => l.SectionID == model.Section).OrderBy(l => l.Name), "ID", "Name").ToList();


            if (MapFile != null)
            {
                if (FileHelper.IsNotValidImage(MapFile))
                {
                    ModelState.AddModelError("Invaalid File Type", "Images must be JPG, GIF, or PNG files.");
                }
            }

            if (ModelState.IsValid)
            {
                if (MapFile != null)
                {
                    var SectionRoute = db.Sections.Where(s => s.ID == model.Section).Select(s => s.Route).First();
                    model.MapFileID = FileHelper.UploadFile("Images/" + SectionRoute + "/Maps/" + MapFile.FileName.ToList(), "site", MapFile);
                }

                if (model.ParentLocation == 0)
                {
                    model.ParentLocation = null;
                }

                var UpdatedLocation = new Location()
                {
                    Description = model.Description,
                    GeographyTypeID = model.GeographyType,
                    ID = model.ID,
                    MapFileID = model.MapFileID,
                    Name = model.Name,
                    ParentLocationID = model.ParentLocation,
                    SectionID = model.Section
                };

                db.Entry(UpdatedLocation).State = EntityState.Modified;
                db.SaveChanges();
                ViewBag.Results = "Location information updated.";
            }

            return View(model);
        }
    }
    catch (Exception ex)
    {
        ErrorSignal.FromCurrentContext().Raise(ex);
        model.Sections = Enumerable.Empty<SelectListItem>();
        ViewBag.Results = "Error updating location informaiton, please try again later.";
        return View(model);
    }
}

This is my Location Entity code:

public class Location
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }

    [Required, Index("IX_Location", 1, IsUnique = true)]
    public string Name { get; set; }

    [Index("IX_Location", 2, IsUnique = true)]
    public Int16 SectionID { get; set; }

    [Column(TypeName = "varchar(MAX)")]
    public string Description { get; set; }

    public Int16 GeographyTypeID { get; set; }
    public int? MapFileID { get; set; }
    public int? ParentLocationID { get; set; }

    [ForeignKey("SectionID")]
    public Section Section { get; set; }

    [ForeignKey("GeographyTypeID")]
    public GeographyType GeographyType { get; set; }

    [ForeignKey("MapFileID")]
    public File Map { get; set; }

    [ForeignKey("ParentLocationID")]
    public Location ParentLocation { get; set; }

    public ICollection<LocationTransitionPoint> TransitionPoints { get; set; }
}

This is my first time trying to update a more complex entity like this but from what I have found on the web I can not see anything wrong.

Hamid Pourjam · Accepted Answer · 2016-10-17T18:51:25.940

16

You can not have two entities (same type) with same primary keys in memory in Entity Framework.

The problem is

model.ParentLocations = new SelectList(db.Locations.Where(l => l.SectionID == model.Section).OrderBy(l => l.Name), "ID", "Name").ToList();

in above line you somehow have loaded the Location which its ID is model.ID

then in

var UpdatedLocation = new Location()
{
    Description = model.Description,
    GeographyTypeID = model.GeographyType,
    ID = model.ID,
    MapFileID = model.MapFileID,
    Name = model.Name,
    ParentLocationID = model.ParentLocation,
    SectionID = model.Section
};
db.Entry(UpdatedLocation).State = EntityState.Modified;

You are creating a new Location and trying to attach it to context (by setting it's state as modified), but you have loaded another Location entity with exact primary key as UpdatedLocation into memory somewhere and this cause the exception.

Try fetching the the location and then change the roperties.

var UpdateLocation = db.Locations.First(l => l.ID == model.ID);
// var UpdateLocation = db.Locations.Find(model.ID); maybe a better option
UpdatedLocation.Description = model.Description;
UpdatedLocation.GeographyTypeID = model.GeographyType;
UpdatedLocation.MapFileID = model.MapFileID;
UpdatedLocation.Name = model.Name;
UpdatedLocation.ParentLocationID = model.ParentLocation;
UpdatedLocation.SectionID = model.Section;

edited Oct 17 '16 at 18:51

answered Sep 12 '15 at 16:42

Hamid Pourjam

20,441
9
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74

Why does this work in the half dozen other update pages I have made so far then? – Matthew Verstraete Sep 12 '15 at 16:50
1

@MatthewVerstraete: take a look at my answer. – Wiktor Zychla Sep 12 '15 at 16:52
3

Because in those pages you have not loaded the entity you want to attach to context in previous lines. But in this situation it causes the specified entity to be loaded in memory. Maybe the line `model.ParentLocations = new SelectList(db.Locations.Where(l => l.SectionID == model.Section).OrderBy(l => l.Name), "ID", "Name").ToList();` – Hamid Pourjam Sep 12 '15 at 16:52
I see now, thanks. As a quick test I moved that call below the save and everything works. – Matthew Verstraete Sep 12 '15 at 17:00
Just a side question, is there any big advantages (other then avoiding the error I ran into) to using your fetch method? – Matthew Verstraete Sep 12 '15 at 17:03
1

If you use `Find` maybe you avoid one additional round-trip to database. – Hamid Pourjam Sep 12 '15 at 17:06
Is there a correct way to release that first resource so I can use Attach again? – Adam Plocher Feb 17 '18 at 00:10

Wiktor Zychla · Answer 2 · 2015-09-12T17:00:43.853

0

Try just getting the entity by id rather than creating a new with fixed id:

var UpdateLocation = db.Locations.FirstOrDefault( l => l.ID == model.ID );

UpdateLocation.Description = model.Description;
...

The reason you see your exception is because your

model.ParentLocations = ...

materializes entities that most probably include the one you try to modify. Thus, the entity is already in the first level cache.

But then you try to pretend yet another entity of the same id exists.

edited Sep 12 '15 at 17:00

answered Sep 12 '15 at 16:43

Wiktor Zychla

47,367
6
74
106

I am sorry but I don't understand what your trying to say the problem is. I think your saying is something to do with `model.ParentLocations =` but I don't understand what your saying the problem with that line is. – Matthew Verstraete Sep 12 '15 at 16:52
This particular line asks the db context to materialize (fetch) some entities and this set includes the entity your model contains. The db context already contains the entity with specified ID. And then you present a newly created object and pretend this is the entity of that ID. EF doesn't allow this, it can't have two entities of the same ID under the same instance of db context. – Wiktor Zychla Sep 12 '15 at 16:55
You should not use `Where` when you are trying to fetch a single entity. – Hamid Pourjam Sep 12 '15 at 16:57
@doctor: sure, you could have edited that obvious typo :) – Wiktor Zychla Sep 12 '15 at 17:01
dv was just a sign! :D +1 – Hamid Pourjam Sep 12 '15 at 17:01
I have two different lines with `model.ParentLocations = ` based off @dotctor post I presume it is the fetch line your talking about and not the reassignment line? – Matthew Verstraete Sep 12 '15 at 17:01
Yes, the one that materializes entities. – Wiktor Zychla Sep 12 '15 at 17:03
@MatthewVerstraete I'm an engineer not **doctor** (dotctor is correct). and yes the problem is in the line which fetches the locations. – Hamid Pourjam Sep 12 '15 at 17:04
2

My apologies, fat fingered your name while typing and eating lunch at the same time. – Matthew Verstraete Sep 12 '15 at 17:07

score 0 · Answer 3 · answered Feb 28 '21 at 22:57

0

i just created a new instance of the contextEntity and the code worked fine

answered Feb 28 '21 at 22:57

hamza felix

39
1
4

1

Welcome to Stack Overflow. Please read How to Answer. https://stackoverflow.com/questions/how-to-answer – Ran Marciano Mar 01 '21 at 05:49

Error attaching entity because of same primary key when trying to save an update

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