Difference Between Select and SelectMany

Question

I\'ve been searching the difference between Select and SelectMany but I haven\'t been able to find a suitable answer. I need to learn the differenc

Answer 1

There are several overloads to SelectMany. One of them allows you to keep trace of any relationship between parent and children while traversing the hierarchy.

Example: suppose you have the following structure: League -> Teams -> Player.

You can easily return a flat collection of players. However you may lose any reference to the team the player is part of.

Fortunately there is an overload for such purpose:

var teamsAndTheirLeagues = 
         from helper in leagues.SelectMany
               ( l => l.Teams
                 , ( league, team ) => new { league, team } )
                      where helper.team.Players.Count > 2 
                           && helper.league.Teams.Count < 10
                           select new 
                                  { LeagueID = helper.league.ID
                                    , Team = helper.team 
                                   };

The previous example is taken from Dan's IK blog. I strongly recommend you take a look at it.