How to get original Entity from ChangeTracker

Question

Is there a way to get the original Entity itself from the ChangeTracker (rather than just the original values)?

If the State is Modified<

Answer 1

Override SaveChanges of DbContext or just access ChangeTracker from the context:

foreach (var entry in context.ChangeTracker.Entries<Foo>())
{
    if (entry.State == System.Data.EntityState.Modified)
    {
        // use entry.OriginalValues
        Foo originalFoo = CreateWithValues<Foo>(entry.OriginalValues);
    }
}

---

Here is a method which will create a new entity with the original values. Thus all entities should have a parameterless public constructor, you can simply construct an instance with new:

private T CreateWithValues<T>(DbPropertyValues values)
    where T : new()
{
    T entity = new T();
    Type type = typeof(T);

    foreach (var name in values.PropertyNames)
    {
        var property = type.GetProperty(name);
        property.SetValue(entity, values.GetValue<object>(name));
    }

    return entity;
}

Answer 2

Nice. Here is a slightly modified version that will handle complex properties:

public static TEntity GetOriginal<TEntity>(this DbContext ctx, TEntity updatedEntity) where TEntity : class
    {
        Func<DbPropertyValues, Type, object> getOriginal = null;
        getOriginal = (originalValues, type) =>
             {
                 object original = Activator.CreateInstance(type, true);
                 foreach (var ptyName in originalValues.PropertyNames)
                 {
                     var property = type.GetProperty(ptyName);
                     object value = originalValues[ptyName];
                     if (value is DbPropertyValues) //nested complex object
                     {
                         property.SetValue(original, getOriginal(value as DbPropertyValues, property.PropertyType));
                     }
                     else
                     {
                         property.SetValue(original, value);
                     }
                 }
                 return original;
             };
        return (TEntity)getOriginal(ctx.Entry(updatedEntity).OriginalValues, typeof(TEntity));
    }

Answer 3

While working with EF 6 i used the following code to get the underlying POCO entity type from proxy type,

var entityType = ObjectContext.GetObjectType(dbEntitymodifiedEntry.Entity.GetType());

ObjectContext.GetObjectType : Return the POCO from proxy object

Answer 4

I would suggest clone entities on materialization and attach them to second context to keep whole original objects graph (if you need it of course). You can make them all ICloneable by modifying T4 template.