yield return slow database calls

Question

In my ASP project there is code like this, to populate rr with RegulationGroups

private IEnumerable<RegulationGroup> LoadRegulations(string moduleName)  
{
    // database calls
    yield return subLrg;
}

In a separate class, the code loops over multiple times

foreach (RegulationGroup rg in rr.RegulationGroups)     
{

}

Each time the code loops over RegulationGroups the database call occurs. How can I avoid the database calls?

I think I can

1. do away with yield return and use a List
2. cache the IEnumerable in a list and use it in my module so that it doesn't affect any other code using the LoadRegulations method.

Answer 1

You can avoid it by materializing the query, f.e. by using ToList():

var regulations = LoadRegulations("moduleName").ToList();

It's due to the nature of deferred execution of the yield return.

What is the purpose/advantage of using yield return iterators in C#?