>>>I need to process all missing Ids. I think this code will only get one of them.
>>
>>Oops:

foreach (var i in itemIds.Where(x => modifierGroup.Items.All(y => y.ItemId != x)))
>>            {
>>                //Use i here
>>            }

>
>So, to be absolutely sure, these two are the same, but the first form is better, right?
>
>

>List<int> itemIds = connection.Query<int>(currentItemsQuery, new { ModGrpId = modifierGroup.GroupId }, transaction).ToList();
>                // Delete list
>                foreach (var id in itemIds.Where(x => modifierGroup.Items.All(y => y.ItemId != x)))
>                {
>                    rowsAffected = connection.Execute(this.deleteQuery, new { ModGrpId = modifierGroup.GroupId, ItemID = id }, transaction);
>                }
>
>                // Delete list
>                foreach (var itemId in itemIds)
>                {
>                    if  (!modifierGroup.Items.Any(x => x.ItemId == itemId))
>                    {                        
>                        rowsAffected = connection.Execute(this.deleteQuery, new { ModGrpId = modifierGroup.GroupId, ItemID = itemId }, transaction);
>                    }
>                }

I think so - but untested.....