无法将实体对象保存到数据库

Question

I am trying to edit an already added entity object.

The model I use for Entity Frameworks` Code First (or Model First, what ever you prefer), is the following:

public class ImageFile
{
    public int Id { get; set; }
    [DisplayName("Naam")]
    public string FileName { get; set; }

    public string ImageUrl { get; set; }
}

In the view I hide the ImageUrl and allow the user to upload a file, which works correctly. After the change of image has happend (this is an Edit method), I want to save the object back into the database.

The following method demonstrates:

public ActionResult Edit([Bind(Include = "Id,FileName,ImageUrl")] ImageFile imageFile, HttpPostedFileBase actualImage)
{
    if(actualImage != null && actualImage.ContentLength > 0)
    {
        ImageFile originalImageFile = db.Images.Find(imageFile.Id);
        if(originalImageFile.FileName != imageFile.FileName)
        {
            DeleteImage(originalImageFile.FileName);
        }
        string fullUrl = SaveImage(imageFile, actualImage);

        // Set the new imageUrl.
        imageFile.ImageUrl = fullUrl.Replace("~", "");

        // Save changes to database
        var entry = db.Entry(imageFile);
        entry.Property(i => i.ImageUrl).IsModified = true;
        entry.Property(i => i.FileName).IsModified = true;
        db.SaveChanges();

        return RedirectToAction("Index");
   }

   // Else that only changes the filename, instead of uploading a new file.
   // Uses same saving logic.

}

As you can see I have changed from the original Edit-savechanges that MVCs' scaffolding created for me. It is something like:

db.Entry(imageFile).State = EntityState.Modified;
db.SaveChanges();

Both solutions didn't work. The first solution throws an InvalidOperationException :

Additional information: Member 'IsModified' cannot be called for property 'ImageUrl' because the entity of type 'ImageFile' does not exist in the context. To add an entity to the context call the Add or Attach method of DbSet.

The second solution also throws an InvalidOperationException :

Additional information: Attaching an entity of type 'BonTemps.Areas.Admin.Models.ImageFile' 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.

I am really stuck here and have no idea what I can do to save the changes. Why will it not save? Does it have anything to do with me setting the ImageUrl manually, after entering the ActionResult method?

Should I create a ViewModel instead, and manually do the changes? Is there any solution in which I can avoid creating a ViewModel for this?

Answer 1

Instead of trying to tell EF that you have changed the properties, use the db Entity that you just pulled from the DB. So the place that you have

// Save changes to database
var entry = db.Entry(imageFile);
entry.Property(i => i.ImageUrl).IsModified = true;
entry.Property(i => i.FileName).IsModified = true;
db.SaveChanges();

Would change to

// Save changes to database
originalImageFile.ImageUrl = imageFile.ImageURL;
originalImageFile.FileName = imageFile.FileName;
db.SaveChanges();