/// <summary>
/// Updates a collection, adding/removing values. The entities in the collection are assumed to be attached/tracked.
/// newValues need not already exist.
/// Also updates the fields of each element.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="collection"></param>
/// <param name="newValues"></param>
/// <param name="context"></param>
public static void UpdateCollectionAndElements <T>(this ICollection <T> collection, IEnumerable <T> newValues, IMyDbContext context) where T : class, IEntity
{
//remove those that need to be removed
var toRemove = collection.Where(x => !newValues.Any(y => y.ID == x.ID)).ToList();
foreach (T item in toRemove)
{
context.SetEntryState(item, EntityState.Deleted);
}
//find the ones that overlap and add or update them
foreach (T item in newValues)
{
if (item.ID == 0) //this means it's newly added
{
collection.Add(item);
}
else //this is an existing entity, update it
{
var attached = collection.FirstOrDefault(x => x.ID == item.ID); //no need for Entry()/Attach() - these are already in the ObjectStateManager
if (attached == null)
{
continue; //if the collection on the server has been changed and the client tries to update a deleted element, you can end up in this scenario...just skip it
}
context.UpdateEntryValues(attached, item);
}
}
}