Question

I am returning two lists from the database using LINQ to SQL compiled query.

While looping the first list I remove duplicates from the second list as I dont want to process already existing objects again.

eg.

//oldCustomers is a List<Customer> returned by my Compiled Linq to SQL Statmenet that I have added a .ToList() at the end to

//Same goes for newCustomers

for (Customer oC in oldCustomers)
{
   //Do some processing
   newCustomers.Remove(newCusomters.Find(nC=> nC.CustomerID == oC.CusomterID));

}

for (Cusomter nC in newCustomers)
{
     //Do some processing
}


DataContext.SubmitChanges()

I expect this to only save the changes that have been made to the customers in my processing and not Remove or Delete any of my customers from the database.

Correct?

I have tried it and it works fine – but I am trying to know if there is any rare case it might actually get removed

Answer 1

Right. When you call .ToList() extension method on any IEnumerable, a new in-memory list of such items is created, without any binding to the previous location of items.

You can add or remove items to/from such a list without fear of some side-effects.

But I have to add that your code is terrible performance-wise.
for (Cusomter nC in newCusomters.Except(oldCustomers)) is much faster and easier to write.