model.cs

public int Save(CollectionViewModel collectionModel)
{
    var collection = collectionModel.Id.HasValue ? _collectionRepository.Get(collectionModel.Id.Value) : new Collection();
    collection.Name = collectionModel.Name;
    collection.Published = collectionModel.Published;
    collection.Featured = collectionModel.Featured;
    collection.Description = collectionModel.Description;
    _collectionRepository.Save(collection);

    return collection.Id;
}