When is the right time to make ToList on an entity framework query - entity-framework

Question

This is called in my service. Now I have asked myself when should I do the .ToList() on the query to materialize the entities?
Do I have to do it at all? Because my application layer will anyway convert the entities to a json array and finally then the enumerator must be enumerated...
Should I follow this thinking? Or is it better to only return a materialized collection to my application layer?
IEnumerable<BrowseSchoolyearDTO> ISchoolyearService.GetAll(int userId)
{
return _context.Schoolyears
.Where(s => s.UserId == userId)
.Select(s => s.ToBrowseSchoolyearDto())
.ToList();
}

Answer 1

You don't need to do a .ToList at all, as long as all your operations on the DTO is done while the db connection is active. You only need to do a .ToList if you need the list to be enumerated and returned outside of the db transaction.
So if your code looks something like this:
Edit: changed repository to service as you don't use repositories
using(var rep = new service())
{
var list = rep.GetAll(1);
return list.Select(x => new DTOViewModel(x)).ToList();
}
you don't need .ToList
If your code looks something like this:
using(var rep = new service())
{
var list = rep.GetAll(1);
}
return list.Select(x => new DTOViewModel(x));
Then you do need a .ToList
Edit to show more of method
public void DoSomeOperationCalledFromWeb(int id)
{
IEnumerable<DTO> list;
using(var serv = new Service())
{
list = rep.GetAll(1).ToList();
/** OR if you need additional filtering **/
list = rep.GetAll(1).Where(/**some filtering**/).ToList();
}
/** Do operations on list **/
}