Update only modified fields in Entity Framework I'm working on a website on ASP.NET MVC4 and EF5. I want to ensure that only modified values are updated in the database.  I'm using a unit of work pattern and repositories for data work. Here's the code for a generic repository. I've two questions, and need a code review for the following code.


Is the code to update only modified fields good? It works, but I don't know if this is the best way. I especially don't like that I have to do this loop through the properties myself (can't EF do this?). I also don't like the cast to object and the comparison.
How are my Add and Update methods? I'm planning the clients (MVC/API controllers) to use a service (passing in a unit of work) to get the work done. They will not directly use the repository. The repository will not have a Save() method, only the UnitOfWork will have one. I can ensure within the service that I will use the same context to update/add entities. Given this, are there any scenarios where my Add/Update code is going to fail?




public class EFRepository&lt;T&gt; : IRepository&lt;T&gt; where T : class
{
    protected DbContext DbContext { get; set; }
    protected DbSet&lt;T&gt; DbSet { get; set; }

    public EFRepository(DbContext dbContext)
    {
        if (dbContext == null)
            throw new ArgumentNullException("dbContext");
        DbContext = dbContext;
        DbSet = DbContext.Set&lt;T&gt;();
    }

    public virtual void Add(T entity)
    {
        DbContext.Entry(entity).State = EntityState.Added;
    }

    public virtual void Update(T entity)
    {
        //dbEntityEntry.State = EntityState.Modified; --- I cannot do this.

        //Ensure only modified fields are updated.
        var dbEntityEntry = DbContext.Entry(entity);
        foreach (var property in dbEntityEntry.OriginalValues.PropertyNames)
        {
            var original = dbEntityEntry.OriginalValues.GetValue&lt;object&gt;(property);
            var current = dbEntityEntry.CurrentValues.GetValue&lt;object&gt;(property);
            if (original != null &amp;&amp; !original.Equals(current))
                dbEntityEntry.Property(property).IsModified = true;
        }
    }

    //... Other methods ...
}
Why bother checking if the value/property has been changed? You are just adding additional complexity for no reason. Sure, it might be slightly! faster to only update modified values, but in return you are adding an overhead to keep track of the modified values, which will diminish whatever performance boost you got. 

Just invoke Update on the entire object... All values that has not been changed will remain the same and the values that has been modified will, well, update.

If it's speed you're looking for you are most likely looking at the wrong place to squeeze ms from.