Entity Framework: ViewModel to Domain Model - asp.net-mvc-3

Question

I'm building an MVC 3 website. I have a model looking like this:
public class Survey
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public DateTime DateStart { get; set; }
public DateTime DateEnd { get; set; }
// Not in view
public DateTime DateCreated { get; set; }
// Not in view
public DateTime DateModified { get; set; }
}
Based on this I also have a View Model to edit the survey information:
public class SurveyEditViewModel
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public DateTime DateStart { get; set; }
public DateTime DateEnd { get; set; }
}
When the user finishes editing I would like to persist the changes. Here's my controller post action:
[HttpPost]
public ActionResult Edit(SurveyEditViewModel model)
{
// Map the view model to a domain model using AutoMapper
Survey survey = Mapper.Map<SurveyEditViewModel, Survey>(model);
// Update the changes
_repository.Update(survey);
// Return to the overview page
return RedirectToAction("Index");
}
In my repository (it's a generic one for now) I have the following code:
public void Update(E entity)
{
using (ABCDataContext context = new ABCDataContext())
{
context.Entry(entity).State = System.Data.EntityState.Modified;
context.SaveChanges();
}
}
When this executes I get the following error: "Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries."
I guess this was to be expected. Mapping from the view model to the model doesn't give me a complete Survey object.
I could modify my controller to look like this. And then it works:
[HttpPost]
public ActionResult Edit(SurveyEditViewModel model)
{
// Map the model to a real survey
survey = _repository.Find(model.Id);
survey.Name = model.Name;
survey.Description = model.Description;
survey.DateStart = model.DateStart;
survey.DateEnd = model.DateEnd;
// Update the changes
_repository.Update(survey);
// Return to the overview page
return RedirectToAction("Index");
}
But I was wondering if a better way is available?

Answer 1

[HttpPost]
public ActionResult Edit(SurveyEditViewModel model)
{
// Fetch the domain model to update
var survey = _repository.Find(model.Id);
// Map only the properties that are present in the view model
// and keep the other domain properties intact
Mapper.Map<SurveyEditViewModel, Survey>(model, survey);
// Update the changes
_repository.Update(survey);
// Return to the overview page
return RedirectToAction("Index");
}