Csharp/CSharp Tutorial/LINQ/Query

All employees in a tree are grouped by department

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }
    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.rupareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }
    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }
        Console.WriteLine(this.NodeData.ToString());
        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }
    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }

    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }
        yield return this.NodeData;
        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}
class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.rupareTo(Employee other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}
class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
        var employeesByDept = empTree.GroupBy(e => e.Department);
        foreach (var dept in employeesByDept)
        {
            Console.WriteLine("Department: {0}", dept.Key);
            foreach (var emp in dept)
            {
                Console.WriteLine("\t{0} {1}", emp.FirstName, emp.LastName);
            }
        }
    }
}

ArrayList Query

using System;
using System.Collections;
using System.ruponentModel;
    public class Product
    {
        string name;
        public string Name
        {
            get { return name; }
        }
        decimal price;
        public decimal Price
        {
            get { return price; }
        }
        public Product(string name, decimal price)
        {
            this.name = name;
            this.price = price;
        }
        public static ArrayList GetSampleProducts()
        {
            ArrayList list = new ArrayList();
            list.Add(new Product("C", 9.99m));
            list.Add(new Product("A", 1.99m));
            list.Add(new Product("F", 2.99m));
            list.Add(new Product("S", 3.99m));
            return list;
        }
        public override string ToString()
        {
            return string.Format("{0}: {1}", name, price);
        }
    }
    class ArrayListQuery
    {
        static void Main()
        {
            ArrayList products = Product.GetSampleProducts();
            foreach (Product product in products)
            {
                if (product.Price > 10m)
                {
                    Console.WriteLine(product);
                }
            }
        }
    }

Chaining Query Operators/extracts all strings containing the letter "a", sorts them by length, and then converts the results to uppercase

using System;
using System.Collections.Generic;
using System.Linq;
class LinqDemo {
    static void Main() {
        string[] names = { "J", "P", "G", "P" };
        IEnumerable<string> query = names
          .Where(n => n.Contains("a"))
          .OrderBy(n => n.Length)
          .Select(n => n.ToUpper());
        foreach (string name in query) Console.Write(name + "|");
    }
}

Complex Query Using Method Syntax

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
    public class Customer
    {
        public string FirstName    { get; set; }
        public string LastName     { get; set; }
        public string EmailAddress { get; set; }
        public override string ToString(){
            return string.Format("{0} {1}\nEmail:   {2}",FirstName, LastName, EmailAddress);
        }
    }
    public class Address
    {
        public string Name   { get; set; }
        public string Street { get; set; }
        public string City   { get; set; }
        public override string ToString()
        {
            return string.Format("{0}, {1}", Street, City);
        }
    }
    public class Tester
    {
        static void Main()
        {
            List<Customer> customers = new List<Customer>
                {
                    new Customer { FirstName = "A", 
                                    LastName = "B",
                                    EmailAddress = "o@a.ru"},
                    new Customer { FirstName = "B", 
                                    LastName = "C",
                                    EmailAddress = "k@a.ru" },
                    new Customer { FirstName = "D", 
                                    LastName = "C",
                                    EmailAddress = "d@a.ru" },
                    new Customer { FirstName = "F", 
                                    LastName = "G",
                                    EmailAddress = "j@a.ru" },
                    new Customer { FirstName = "L", 
                                    LastName = "H",
                                    EmailAddress = "l@a.ru" }
                };
            List<Address> addresses = new List<Address>
                {
                    new Address { Name   = "J",
                                  Street = "165 Main", 
                                    City = "City 1" },
                    new Address { Name   = "K H",
                                  Street = "3207 Way", 
                                    City = "Cith 2" },
                    new Address { Name   = "J G",
                                  Street = "800 Blvd.", 
                                    City = "City 3" },
                    new Address { Name   = "Mary",
                                  Street = "7 Ave", 
                                    City = "City 4" },
                    new Address { Name   = "Kate",
                                  Street = "2251 Avenue", 
                                    City = "City 5" }
                };
            var result = customers.Join(addresses,
                        customer => string.Format("{0} {1}", customer.FirstName, customer.LastName),
                        address => address.Name,
                        (customer, address) => new { Customer = customer, Address = address })
                        .OrderBy(ca => ca.Customer.LastName)
                        .ThenByDescending(ca => ca.Address.Street);
            foreach (var ca in result)
            {
                Console.WriteLine(string.Format("{0}\nAddress: {1}",ca.Customer, ca.Address));
            }
        }
    }

Conduct query on the result again

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

    class Customer
    {
        public string ID { get; set; }
        public string City { get; set; }
        public string Country { get; set; }
        public string Region { get; set; }
        public decimal Sales { get; set; }
    }
    class Program
    {
        static void Main(string[] args)
        {
            List<Customer> customers = new List<Customer> {
              new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 },
              new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 },
              new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 }
           };
            var queryResults =
                from c in customers
                group c by c.Region into cg
                select new { TotalSales = cg.Sum(c => c.Sales), Region = cg.Key }
               ;
            var orderedResults =
                from cg in queryResults
                orderby cg.TotalSales descending
                select cg
             ;
            foreach (var item in orderedResults)
            {
                Console.WriteLine(item.TotalSales + "\t: " + item.Region);
            }
        }
    }

Get Distinct departments with condition

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }
    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.rupareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }
    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }
        Console.WriteLine(this.NodeData.ToString());
        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }
    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }

    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }
        yield return this.NodeData;
        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}
class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.rupareTo(Employee other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}
class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
        var depts = empTree.Select(d => d.Department).Distinct();
        foreach (var dept in depts)
            Console.WriteLine("Department: {0}", dept);
    }
}

Join Query

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
    class Customer
    {
        public string ID { get; set; }
        public string City { get; set; }
        public string Country { get; set; }
        public string Region { get; set; }
        public decimal Sales { get; set; }
    }
    class Order
    {
        public string ID { get; set; }
        public decimal Amount { get; set; }
    }
    class Program
    {
        static void Main(string[] args)
        {
            List<Order> orders = new List<Order> {
              new Order { ID="X", Amount=900 },
              new Order { ID="Y", Amount=1000 },
              new Order { ID="Z", Amount=1100 }
            };
            List<Customer> customers = new List<Customer> {
              new Customer { ID="X", City="Beijing", Country="China", Region="Asia", Sales=9000 },
              new Customer { ID="Y", City="Bogot&aacute;", Country="Colombia", Region="South America", Sales=1001 },
              new Customer { ID="Z", City="Lima", Country="Peru", Region="South America", Sales=2002 }
           };
            var queryResults =
               from c in customers
               join o in orders on c.ID equals o.ID
               select new { c.ID, c.City, SalesBefore = c.Sales, NewOrder = o.Amount, SalesAfter = c.Sales+o.Amount };
            foreach (var item in queryResults)
            {
                Console.WriteLine(item);
            }
        }
    }

query with extension methods

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
    public class Customer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string EmailAddress { get; set; }
        public override string ToString()
        {
            return string.Format("{0} {1}\nEmail:   {2}",FirstName, LastName, EmailAddress);
        }
    }
    public class Tester
    {
        static void Main()
        {
            List<Customer> customers = new List<Customer>{
                    new Customer { FirstName = "A", 
                                    LastName = "B",
                                    EmailAddress = "o@a.ru"},
                    new Customer { FirstName = "B", 
                                    LastName = "C",
                                    EmailAddress = "k@a.ru" },
                    new Customer { FirstName = "D", 
                                    LastName = "C",
                                    EmailAddress = "d@a.ru" },
                    new Customer { FirstName = "F", 
                                    LastName = "G",
                                    EmailAddress = "j@a.ru" },
                    new Customer { FirstName = "L", 
                                    LastName = "H",
                                    EmailAddress = "l@a.ru" }
                };
            IEnumerable<Customer> result = customers.Where(customer => customer.FirstName == "Donna");
            foreach (Customer customer in result)
                Console.WriteLine(customer.ToString());
        }
    }

Use a LINQ query to find the public enums

using System;
using System.Reflection;
using System.IO;
using System.Linq;
  public class MainClass
  {
    static void Main(string[] args)
    {
      string displayName = null;
      displayName = "System.Windows.Forms,Version=2.0.0.0,PublicKeyToken=b77a5c561934e089,Culture=\"\"";
      Assembly a = Assembly.Load(displayName);
      Type[] types = a.GetTypes();
      var publicEnums = from pe in types where pe.IsEnum && pe.IsPublic select pe;
      foreach (var pe in publicEnums)
      {
        Console.WriteLine(pe);
      }
    }
  }

Use Contains, Length and ToUpper from Linq

using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {
        string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" };
        IEnumerable<string> filtered = names.Where(n => n.Contains("a"));
        IEnumerable<string> sorted = filtered.OrderBy(n => n.Length);
        IEnumerable<string> finalQuery = sorted.Select(n => n.ToUpper());
        foreach (string name in filtered)
            Console.Write(name + "|");        
        Console.WriteLine();
        foreach (string name in sorted)
            Console.Write(name + "|");        
        Console.WriteLine();
        foreach (string name in finalQuery)
            Console.Write(name + "|");        
    }
}

Use from where select to choose the Employees in the IT department from a tree

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }
    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.rupareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }
    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }
        Console.WriteLine(this.NodeData.ToString());
        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }
    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }

    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }
        yield return this.NodeData;
        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}
class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.rupareTo(Employee other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}
class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
        var ITEmployees = from e in empTree
                          where String.Equals(e.Department, "IT")
                          select e;
        foreach (var emp in ITEmployees)
            Console.WriteLine(emp);
    }
}

Use LINQ to get Employees in the IT department from a tree

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }
    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.rupareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }
    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }
        Console.WriteLine(this.NodeData.ToString());
        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }
    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }

    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }
        yield return this.NodeData;
        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}
class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.rupareTo(Employee other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}
class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
        var ITEmployees = empTree.Where(e => String.Equals(e.Department, "IT")).Select(emp => emp);
        foreach (var emp in ITEmployees)
            Console.WriteLine(emp);
    }
}

Use select to retrieve all nodes in a Binary tree

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }
    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.rupareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }
    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }
        Console.WriteLine(this.NodeData.ToString());
        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }
    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }

    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }
        yield return this.NodeData;
        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}
class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }
    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.rupareTo(Employee other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}
class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });
        var allEmployees = from e in empTree.ToList<Employee>()
                           select e;
        foreach (var emp in allEmployees)
            Console.WriteLine(emp);
    }
}