Difference Between Select and SelectMany

Question

Hi,

I've been searching the difference between those two but I couldn't find actually what I want. I need learn the difference when using LINQ To SQL but they all gave me standard array examples.

Can some one give a LINQ TO SQL Example to show the difference between Select and Select Many.

Thanks in advance.

Answer 1

I understand SelectMany to work like an join shortcut.

So you can:

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

Answer 2

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

EDIT: since I'm apparently unable to craft a legal LINQ query when I haven't eaten, I'll defer to this blog post to explain further.

Answer 3

SelectMany flattens queries that return lists of lists. For example

public class PhoneNumber
{
    public string Number { get; set; }
}

public class Person
{
    public IEnumerable<PhoneNumber> PhoneNumbers { get; set; }
}

IEnumerable<Person> people = new List<Person>();

// Select gets a list of lists of phone numbers
IEnumerable<IEnumerable<PhoneNumber>> phoneLists = people.Select(p => p.PhoneNumbers);

// SelectMany flattens it to just a list of phone numbers.
IEnumerable<PhoneNumber> phoneNumbers = people.SelectMany(p => p.PhoneNumbers);