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

var players = db.SoccerTeams.Where(c => c.Country == "Spain")
                            .SelectMany(c => c.players);

foreach(var player in players)
{
    Console.WriteLine(player.LastName);
}

1. De Gea
2. Alba
3. Costa
4. Villa
5. Busquets

...

Answer 2

Select is a simple one-to-one projection from source element to a result element. Select- Many is used when there are multiple from clauses in a query expression: each element in the original sequence is used to generate a new sequence.

Answer 3

Without getting too technical - database with many Organizations, each with many Users:-

var orgId = "123456789";

var userList1 = db.Organizations
                   .Where(a => a.OrganizationId == orgId)
                   .SelectMany(a => a.Users)
                   .ToList();

var userList2 = db.Users
                   .Where(a => a.OrganizationId == orgId)
                   .ToList();

both return the same ApplicationUser list for the selected Organization.

The first "projects" from Organization to Users, the second queries the Users table directly.

Answer 4

I understand SelectMany to work like a join shortcut.

So you can:

var orders = customers
             .Where(c => c.CustomerName == "Acme")
             .SelectMany(c => c.Orders);

Answer 5

SelectMany() lets you collapse a multidimensional sequence in a way that would otherwise require a second Select() or loop.

More details at this blog post.