Question

I have a hard time telling what operations in linq cause a SQL command to be issued to the database.

I know calling ToList() or iterating w/ foreach will cause the query to run but do Select and GroupBy cause the code to execute on the database?

Answer 1

No, they don’t, if they’re correctly called on the IQueryable rather than the IEnumerable, they are compiled as expressions and will later be translated to SQL.

You can use the intellisense tooltip to see which will be the currently called method. If the first parameter of the extension method is IEnumerable rather than IQueryable, you’ll run into a database query.