Question

i’m not sure this is the best way to do the following code. I’m not sold on a foreach inside another foreach. Could this be done *better** with Linq?

*I understand that better could be either
a) more performant
b) easier to read / more elegant
c) all of the above

NOTE: .NET 3.5 solutions accepted 🙂 NOTE2: the two IList’s were the results of a multi-recordset stored procedure, via Linq2Sql.

here’s the make believe code:

// These two lists are the results from a IMultipleResults Linq2Sql stored procedure. IList<Car> carList = results.GetResult<Car>().ToList(); IList<Person> people = results.GetResult<Person>().ToList();  // Associate which people own which cars. foreach(var person in people) {     var cars = (from c in cars                 where c.CarId == person.CarId                 select c).ToList();      foreach (var car in cars)     {         car.Person = person;         } } 

Cheers 🙂

Answer 1

I don’t think performance would be any different but if you’re looking for terseness:

var q = from person in people         join car in cars on person.CarId equals car.CarId         select new { car, person }; foreach(var o in q) {   o.car.Person = o.person;  } 

Edit: After Jon’s hint on this version being faster I got curious and profiled both functions. This version seems twice as fast which is amazing. I checked the disassembly. The overhead of the original implementation seems to come from new enumerators getting created for both outer and inner loop, causing P times new/dispose overhead.

For this code only one Enumerator is created which I think is the magic of ‘Join’ function. I didn’t examine how it works though.