EF 4.2 Update POCO with ObjectContext
Posted By Mike Bender / 10th February 2012
I recently worked on a project that used the Entity Framework and T4 POCO generation. I ran into a little snag during the implementation of the Repository pattern that took a few minutes for me to figure so I thought that I would save someone else the time and share here.
First let’s start off with the Interface.
public interface IRepository : IDisposable
{
IQueryable All { get; }
T GetById(int id);
void Add(T model);
void Update(T model);
void Delete(T model);
void Save();
}
Next we’ll look at my first try at the concrete implementation of the Update method. The DataContext is a private property containing a reference to the object context object.
public class MyRepository : IRepository
{
public IQueryable All { get{...} }
public MyEntity GetById(int id) {...}
public void Add(MyEntity model) {...}
public void Update(MyEntity model)
{
DataContext.Users.Attach(model);
if (model.Id == null )
{
// no UserId denotes new object to the database.
DataContext.ObjectStateManager.ChangeObjectState(model, System.Data.EntityState.Added);
}
else
{
// object is not new. We need to get the original object and apply original values.
// Applying current or original values, changes the state
// of the attached object to Modified.
var originalObject = GetById(model.UserId);
DataContext.ApplyCurrentValues("MyEntities", originalObject);
}
Save();
}
public void Delete(MyEntity model) {...}
public void Save() {...}
}
Everything looked good to me so I ran a quick test set. To my surprise the Update method was failing. Why would this be? Well as it turns out since I was generating my POCO’s I needed to set the EntityState to Modified manually. So added the line below after the ApplyCurrentValues call.
DataContext.ObjectStateManager.ChangeObjectState(model, System.Data.EntityState.Modified);
I fired up the test cases once again and was happy to see all tests passed.
Well that is it, I hope that this post helps you and others in the future.
