What is the best way to prevent updating on specific fields in Entity Framework

Question

Im writing an web application with MVC using Entity Framework for my backend logic. My problem is that I have an entity that has certain fields that should never be changed on an update. I am not really sure what the best way to solve this problem would be. There is going to be a lot of data processed in my application, so I cant afford to just hack up a solution.

Is it possible to just define the fields as readonly in the POCO entities ? Or should I write and entity framework extension class that validates all updates. Could it be done in the mapping files between EF and the actual database?

I am relatively new with EF, so I hope some of you might be able to give me some pointers!

Thanks!

Answer 1

If you are using .NET 4.5 and EF 5 (i.e. MVC 4), you can simply set IsModified = false on the individual properties in question. This has the benefit of sticking close to the default out-of-the-box MVC conventions.

For example, if you have a CreatedBy field that shouldn't be touched when the record is updated, use the following in your controller:

[HttpPost]
    public ActionResult Edit(Response response)
    {
        if (ModelState.IsValid)
        {
            db.Entry(response).State = EntityState.Modified;
            db.Entry(response).Property(p => p.CreatedBy).IsModified = false;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(response);
    }

Note that the IsModified line is the only change from the default controller action.

You MUST put this line AFTER setting .State = EntityState.Modified (which applies to the record as a whole and adds the record into the db context).

The effect is that EF will not include this column in the SQL UPDATE statement.

I am still (very) shocked that there are no [InsertOnly] or [UpdateOnly] attributes similar to [ReadOnly]. This seems like a major oversight by the MVC team. Am I missing something?

I'm not fully satisfied with this solution because it's a hack: You're telling EF that no change was made when what you really mean to say is "HANDS OFF". It also means that you have to use this code anyplace where the field could be updated. It would be better to have an attribute on the class property.

(Apologies for posting to an older thread, but I've not see this solution anywhere else. ViewModels are robust but a lot of work, and EF was supposed to make things easier, not harder...)