using System;

using System.Linq;

​

​

public class AccountDto 

{

    public int AccountId { get; set; }

    public string AccountName { get; set; }

    public bool Selected { get; set; }

}

​

public class AreaDto

{

    public string AreaName { get; set; }

    public AccountDto[] Accounts { get; set; }

}

public class Program

{

    public static void Main()

    {

        var areas = new AreaDto[] 

        {

            new AreaDto 

            {

                AreaName = "Philippines",

                Accounts = new AccountDto[]

                {

                    new AccountDto 

                    {

                        AccountId = 168,

                        AccountName = "Account 168",

                        Selected = true

                    },

                    new AccountDto 

                    {

                        AccountId = 169,

                        AccountName = "Account 169",

                        Selected = true

                    },

                }

            },

            new AreaDto 

            {

                AreaName = "China",

                Accounts = new AccountDto[]

                {

                    new AccountDto 

                    {

                        AccountId = 170,

                        AccountName = "Account 170"

                    },

                    new AccountDto 

                    {

                        AccountId = 171,

                        AccountName = "Account 171",

                        Selected = true 

                    },

                }

            },

        };

        var result = 

            from account in areas.SelectMany(area => area.Accounts)

            where account.Selected

            select account.AccountId;

        result.Dump();

    }

}

​