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I'm making a survey program that has a list of questions that are pulled from the database as entities. During the course of the survey the properties of the entity may be edited, but I do not want these changes persisted to the database. So, I detach the questions after they are loaded into the dbcontext and access them via a dictionary.

The problem arises when I attempt to save an answer to the database. Since the answer entity is related to the question entity (that has been detached) a completely new question entity is then added to the database. I'm not sure why this is occurring as the answer entity being added contains the proper ID of the detached entity (when I look at it in the debugger). However, upon saving changes it gets updated to the ID of the newly created duplicate entity.

Is there a way to stop this behavior? Or alternatively, is there a way to make changes to an entity and not have them persist to the database even when SaveChanges is called on the context for writing a answer or a log entry to the database?

Here is the code that loads, then detatches the questions (items):

 public FixedLengthBlockElementRuntime(FixedLengthBlock block, RuntimeContext context) : base(block, context)
    {
        this._items = ((FixedLengthBlock)this.Element).ItemBank.Items.OfType<FixedLengthItem>().ToDictionary(x => x.ItemName, x => x);


        foreach(FixedLengthItem fixedLengthItem in this._items.Values)
        {
            this.Context.DetachEntity(fixedLengthItem);
        }
    }

And here is the code that adds the duplicate entry:

    public void SetResponse(Response response)
    {
        response.Session = this.Session;
        this.DbContext.Responses.AddObject(response);
        this.DbContext.SaveChanges();
    }

Note that Response has the proper ItemId until the point of Saving Changes.

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  • Where do you connect the question to the answer? Commented Aug 28, 2012 at 15:37
  • Via an association in the edmx file. So I believe it is automatic. Commented Aug 28, 2012 at 15:39

1 Answer 1

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You can set the MergeOption on your questions DbSet to be OverwriteChanges.

Context.Questions.MergeOption = MergeOption.OverwriteChanges;

You'll need to be sure you set that BEFORE you make the query for the questions for this to work properly however.

More reading on how MergeOptions work

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4 Comments

Sorry, I had gone down a CF route - updated with a better answer for model first
This was not working. I started to go down that road though. Is there a way to leave the entity attached but ignore any changes that may have occurred to it while saving to the database? I thought something like 'DbContext.Items.ApplyOriginalValues' would do the trick, but it did not work.
One thought would be to set the mergeoption to overwrite changes...then reload the item from the DB before saving the response? It works, but feels inefficient...any ideas?
You could use the Refresh method to reload the entity from the DB prior to saving changes. DbContext.Refresh( RefreshMode.StoreWins, question );

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