Adding a relation object in a generic / abstract way

I am trying to write a WCF method that will receive a separate EntityObject client from the client and be able to determine which properties and which relationships have changed for that object, comparing it to what is already in the context. Of course, if this object is a new entity or one of its relationships has been added / removed / changed, it must also recognize this and act accordingly.

I can already find out if the entity relation is new, but can't seem to add it correctly. -With any approach I am trying to get another exception.

Here is the method I use to update a single object:

public static void AttachUpdated(this ObjectContext context, EntityObject objectDetached)
{
    if (objectDetached.EntityState == EntityState.Detached)
    {
        object currentEntityInDb = null;

        if (context.TryGetObjectByKey(objectDetached.EntityKey, out currentEntityInDb))
        {
            context.ApplyPropertyChanges(objectDetached.EntityKey.EntitySetName, objectDetached);
            //Apply property changes to all referenced entities in context 
            context.ApplyReferencePropertyChanges((IEntityWithRelationships)objectDetached,
                                                  (IEntityWithRelationships)currentEntityInDb); //Custom extensor method 
        }
        else
        {
            //The entity should be added
            //?????
        }
    }
}

      

        
        
        
      

    

And this is the method I use to update entity relationships:

public static void ApplyReferencePropertyChanges(this ObjectContext context,
                                                         IEntityWithRelationships newEntity,
                                                         IEntityWithRelationships oldEntity)
{
    foreach (var oldRelatedEnd in oldEntity.RelationshipManager.GetAllRelatedEnds())
    {
        var oldRef = oldRelatedEnd as EntityReference;

        if (oldRef != null)
        {
            // this related end is a reference not a collection 
            var newRef = newEntity.RelationshipManager.GetRelatedEnd(oldRef.RelationshipName, oldRef.TargetRoleName) as EntityReference;
            if (newRef.EntityKey != null)
            {
                oldRef.EntityKey = newRef.EntityKey;
            }
            else
            {   
                //When oldRed is a 1:Many relationship
                //newRef is an EntityReference<TEntity> object
                EntityObject entity = newRef.GetType().GetProperty("Value").GetValue(newRef, null) as EntityObject;
                oldRef.EntityKey = entity.EntityKey;
            }
        }
        else
        {
            IRelatedEnd newRelatedEnd = newEntity.RelationshipManager.GetRelatedEnd(oldRelatedEnd.RelationshipName, oldRelatedEnd.TargetRoleName);
            foreach (IEntityWithRelationships e in newRelatedEnd)
            {
                if (!oldRelatedEnd.Contains((e as IEntityWithKey).EntityKey))
                {
                    //this is a new relation and it needs to be added.
                    //???????
                }
                else
                {
                    //Find out if relation was modified - and update it if needed
                    //????????
                }
            }
            IEnumerable entities = oldRelatedEnd as IEnumerable;

        }
    }
}

      

        
        
        
      

    

How should this be done?

Please, help: (