I have the following update method in my generic Repository

```
public class Repository<T> : IRepository<T> where T : class
{
    private readonly DbSet<T> _dbSet;
    public virtual T Update(T item) {
        return _dbSet.Attach(item);
    }
}

```

the `UnitOfWork` has a commit method which calls the `SaveChanges` on the context. More details here  

<https://codereview.stackexchange.com/questions/19037/entity-framework-generic-repository-pattern>

When I update an entity and then call

```
ProductRepository.Update(modifiedProduct);
UnitOfWork.Commit;

```

Nothing floats down to the database.

However , Merely calling the Commit works ( no call to the update method ).

So, what is the Attach Method doing that causes the changes to not flow down to the database.
I think the attach call is the correct call to make in the Update Method. So, what is causing the unexpected behavior.

From the EF Source code on CodePlex 

```
/// <summary>
///     Attaches the given entity to the context underlying the set.  That is, the entity is placed
///     into the context in the Unchanged state, just as if it had been read from the database.
/// </summary>
/// <param name="entity"> The entity to attach. </param>
/// <returns> The entity. </returns>
/// <remarks>
///     Attach is used to repopulate a context with an entity that is known to already exist in the database.
///     SaveChanges will therefore not attempt to insert an attached entity into the database because
///     it is assumed to already be there.
///     Note that entities that are already in the context in some other state will have their state set
///     to Unchanged.  Attach is a no-op if the entity is already in the context in the Unchanged state.
/// </remarks>
public object Attach(object entity)
{
    Check.NotNull(entity, "entity");

    InternalSet.Attach(entity);
    return entity;
}

```