Question

I came to this site searching for object comparison in Dictionary, and i came to know that overriding GetHashCode and Equals are a must for doing object comparison in C#.
Here is a piece of code that i have been trying to solve out, using FOREACH iteration Method. But my Boss says to do the same without using any iteration(maybe by using containskey or containsvalue method), due to performance issues. Any help is highly welcome..

  public class employee
    {
        public string empname { get; set; }
        public string location { get; set; }
        public double kinid { get; set; }
        public double managerKin { get; set; }
        public override bool Equals(object obj)
        {
            return base.Equals(obj);
        }
        public override int GetHashCode()
        {
            return base.GetHashCode();
        }
    }

    public class manager
    {
        public string managername { get; set; }
        public double kinid { get; set; }

        public override int GetHashCode() 
        { 
          return 17 * managername.GetHashCode() + kinid.GetHashCode();
        }
    }
    public class program
    {
        public static void Main()
        {
            employee emp = new employee();
            employee emp2 = new employee();
            manager mng = new manager();
            manager mng2 = new manager();

            emp.empname = "Deepak";
            emp.location = "Pune";
            emp.kinid = 36885;
            emp.managerKin = 007;


            emp2.empname = "Astha";
            emp2.location = "Pune";
            emp2.kinid = 30000;
            emp2.managerKin = 007;

            mng.kinid = 007;
            mng.managername = "Gaurav";
            mng2.kinid = 001;
            mng2.managername = "Surya";

            Dictionary<employee, manager> relations = new Dictionary<employee, manager>();
            relations.Add(emp, mng);
            relations.Add(emp2, mng2);

            Console.ForegroundColor = ConsoleColor.Yellow;
            Console.WriteLine("The Manager details are :");
            foreach (var element in relations)
            Console.WriteLine(" \n KINID : {0} \n  Manager'sName :                    {1}",element.Value.kinid, element.Value.managername);
            Console.WriteLine("Enter the details of the manager..");
            Console.ForegroundColor = ConsoleColor.Gray;
            Console.Write("\nManager's Kin : ");
            double mkin = Convert.ToDouble(Console.ReadLine());

            Console.Write("Manager's Name : ");
            string mname = Console.ReadLine();

            manager mng1 = new manager();
            mng1.kinid = mkin;
            mng1.managername = mname;
            int hashvalue = 17 * mname.GetHashCode() + mkin.GetHashCode();



            #region BY USING FOREACH LOOP
            int i = 0;
            foreach (var element in relations)
            {
                if (element.Value.GetHashCode() == hashvalue)
                {
                    i += 1;
                    if (i == 1)
                    {
                        Console.WriteLine("The Following employees report to the Manager : {0}", mname);

                    }
                    Console.WriteLine(element.Key.empname + " " + element.Key.kinid + " " + element.Key.location + " " + element.Key.managerKin);

                }
            }
            if (i == 0)
            {
                Console.WriteLine("sorry the manager's details you entered \"{0}\" \"{1}\" does not exist in our database..", mng1.managername, mng1.kinid);

            }
            #endregion

            Console.ReadLine();
        }

    }

Answer 1

For searching an object in a dictionary using the ContainsKey or ContainsValue keyword, compiler uses two implicit functions i.e. GetHashCode() and Equals(). So when we have an object for comparison, we need to Override both these methods !!

Here is the code

#region USING DICTIONARY TO STORE CLASS OBJECTS (check employee existence and print manager's name)
public class employee
{
    public string empname { get; set; }
    public string location { get; set; }
    public double kinid { get; set; }
    public double managerKin { get; set; }

    //public override bool Equals(object obj) // ANY OF THE TWO EQUALS METHOD WORKS.
    //{
    //    employee otheremployee;
    //    otheremployee = (employee)obj;
    //    return (otheremployee.kinid == this.kinid && otheremployee.location == this.location && otheremployee.empname == this.empname && otheremployee.managerKin == this.managerKin);

    //}
    public override bool Equals(object obj)   //When Running this entire code, put a break-point on both the Equals() and GetHashCode() methods, and see the execution flow.
    {
        employee otheremployee;
        otheremployee = (employee)obj;
        return (obj.GetHashCode() == otheremployee.GetHashCode());

    }
    public override int GetHashCode()    //When Running this entire code, put a break-point on both the Equals() and GetHashCode() methods, and see the execution flow.
    {
        //int temp = base.GetHashCode(); // DONT USE THIS
        //return base.GetHashCode();
        int temp = empname.GetHashCode() + location.GetHashCode() + kinid.GetHashCode() + managerKin.GetHashCode();
        return temp;
    }
}

public class manager
{
    public string managername { get; set; }
    public double kinid { get; set; }


   
    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
    public override bool Equals(object obj)
    {
        return base.Equals(obj);
    }
}
public class program
{
    public static void Main()
    {
        employee emp = new employee();
        employee emp2 = new employee();
        manager mng = new manager();
        manager mng2 = new manager();

        emp.empname = "Deepak";
        emp.location = "Pune";
        emp.kinid = 36885;
        emp.managerKin = 007;


        emp2.empname = "Astha";
        emp2.location = "Pune";
        emp2.kinid = 30000;
        emp2.managerKin = 001;

        mng.kinid = 007;
        mng.managername = "Gaurav";
        mng2.kinid = 001;
        mng2.managername = "Surya";

        Dictionary<employee, manager> relations = new Dictionary<employee, manager>();
        relations.Add(emp, mng); // put a BreakPoint here and see the execution flow
        relations.Add(emp2, mng2);// put a BreakPoint here and see the execution flow

        Console.ForegroundColor = ConsoleColor.Yellow;
        Console.WriteLine("The Employee details are :");
        foreach (var element in relations)
            Console.WriteLine(" \n Employee Name : {0} \n Location : {1} \n Employee KinId : {2} \n Manager's KinId : {3} ",
                element.Key.empname, element.Key.location, element.Key.kinid, element.Key.managerKin);

        Console.WriteLine("Enter the details of the Employee..");
        Console.ForegroundColor = ConsoleColor.Gray;
        Console.Write("\nEmployee Name : "); string ename = Console.ReadLine();
        Console.Write("Location : "); string elocn = Console.ReadLine();
        Console.Write("Employee KinId : "); double ekinid = Convert.ToDouble(Console.ReadLine());
        Console.Write("Manager's ID : "); double emngr = Convert.ToDouble(Console.ReadLine());
        employee emp1 = new employee();
        emp1.empname = ename;
        emp1.location = elocn;
        emp1.kinid = ekinid;
        emp1.managerKin = emngr;


        int i = 0; // This variable acts as a indicator to find whether the Employee Key exists or not.
        if (relations.ContainsKey(emp1)) //Put a break point here and see the execution flow.
        {
            Console.WriteLine("the Employee : {0} exists..", emp1.empname);
            Console.WriteLine("the Employee reports to the following manager : {0} \n and the Manager's KinId is {1}.", (relations[emp1]).managername, relations[emp1].kinid);
            i = 1;
            Console.ReadLine();
        }

        if (i == 0)
        {
            Console.WriteLine("the details of the employee named {0} does not exist !!", emp1.empname);
            Console.ReadLine();
        }

#endregion