C# Facade Design Pattern

A visualization of the classes and objects participating in this pattern.

The classes and objects participating in this pattern include:

• Facade   (MortgageApplication)
  • knows which subsystem classes are responsible for a request.
  • delegates client requests to appropriate subsystem objects.
• Subsystem classes   (Bank, Credit, Loan)
  • implement subsystem functionality.
  • handle work assigned by the Facade object.
  • have no knowledge of the facade and keep no reference to it.

This structural code demonstrates the Facade pattern which provides a simplified and uniform interface to a large subsystem of classes.

using System;

namespace Facade.Structural
{
    /// <summary>
    /// Facade Design Pattern
    /// </summary>

    public class Program
    {
        public static void Main(string[] args)
        {
            Facade facade = new Facade();

            facade.MethodA();
            facade.MethodB();

            // Wait for user

            Console.ReadKey();
        }
    }

    /// <summary>
    /// The 'Subsystem ClassA' class
    /// </summary>

    public class SubSystemOne
    {
        public void MethodOne()
        {
            Console.WriteLine(" SubSystemOne Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassB' class
    /// </summary>

    public class SubSystemTwo
    {
        public void MethodTwo()
        {
            Console.WriteLine(" SubSystemTwo Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassC' class
    /// </summary>

    public class SubSystemThree
    {
        public void MethodThree()
        {
            Console.WriteLine(" SubSystemThree Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassD' class
    /// </summary>

    public class SubSystemFour
    {
        public void MethodFour()
        {
            Console.WriteLine(" SubSystemFour Method");
        }
    }

    /// <summary>
    /// The 'Facade' class
    /// </summary>

    public class Facade
    {
        SubSystemOne one;
        SubSystemTwo two;
        SubSystemThree three;
        SubSystemFour four;

        public Facade()
        {
            one = new SubSystemOne();
            two = new SubSystemTwo();
            three = new SubSystemThree();
            four = new SubSystemFour();
        }

        public void MethodA()
        {
            Console.WriteLine("\nMethodA() ---- ");
            one.MethodOne();
            two.MethodTwo();
            four.MethodFour();
        }

        public void MethodB()
        {
            Console.WriteLine("\nMethodB() ---- ");
            two.MethodTwo();
            three.MethodThree();
        }
    }
}

Output

This real-world code demonstrates the Facade pattern as a MortgageApplication object which provides a simplified interface to a large subsystem of classes measuring the creditworthiness of an applicant.

using System;

namespace Facade.RealWorld
{
    /// <summary>
    /// Facade Design Pattern
    /// </summary>

    public class Program
    {
        public static void Main(string[] args)
        {
            // Facade

            Mortgage mortgage = new Mortgage();

            // Evaluate mortgage eligibility for customer

            Customer customer = new Customer("Ann McKinsey");
            bool eligible = mortgage.IsEligible(customer, 125000);

            Console.WriteLine("\n" + customer.Name +
                    " has been " + (eligible ? "Approved" : "Rejected"));

            // Wait for user

            Console.ReadKey();
        }
    }

    /// <summary>
    /// The 'Subsystem ClassA' class
    /// </summary>

    public class Bank
    {
        public bool HasSufficientSavings(Customer c, int amount)
        {
            Console.WriteLine("Check bank for " + c.Name);
            return true;
        }
    }

    /// <summary>
    /// The 'Subsystem ClassB' class
    /// </summary>

    public class Credit
    {
        public bool HasGoodCredit(Customer c)
        {
            Console.WriteLine("Check credit for " + c.Name);
            return true;
        }
    }

    /// <summary>
    /// The 'Subsystem ClassC' class
    /// </summary>

    public class Loan
    {
        public bool HasNoBadLoans(Customer c)
        {
            Console.WriteLine("Check loans for " + c.Name);
            return true;
        }
    }

    /// <summary>
    /// Customer class
    /// </summary>

    public class Customer
    {
        private string name;

        // Constructor

        public Customer(string name)
        {
            this.name = name;
        }

        public string Name
        {
            get { return name; }
        }
    }

    /// <summary>
    /// The 'Facade' class
    /// </summary>

    public class Mortgage
    {
        Bank bank = new Bank();
        Loan loan = new Loan();
        Credit credit = new Credit();

        public bool IsEligible(Customer cust, int amount)
        {
            Console.WriteLine("{0} applies for {1:C} loan\n",
                cust.Name, amount);

            bool eligible = true;

            // Check creditworthyness of applicant

            if (!bank.HasSufficientSavings(cust, amount))
            {
                eligible = false;
            }
            else if (!loan.HasNoBadLoans(cust))
            {
                eligible = false;
            }
            else if (!credit.HasGoodCredit(cust))
            {
                eligible = false;
            }

            return eligible;
        }
    }
}

Output

The .NET optimized code demonstrates the same code as above but uses more modern C# and .NET features.

Here is an elegant C# Facade solution.

namespace Facade.NetOptimized;

using static System.Console;

/// <summary>
/// Facade Design Pattern
/// </summary>
public class Program
{
    static void Main()
    {
        // Facade
        var mortgage = new Mortgage();

        // Evaluate mortgage eligibility for customer
        var customer = new Customer("Ann McKinsey");
        bool eligible = mortgage.IsEligible(customer, 125000);

        string result = eligible ? "Approved" : "Rejected";
        WriteLine($"\n{customer.Name} has been {result}");


        // Wait for user
        ReadKey();
    }
}

/// <summary>
/// The 'Subsystem ClassA' class
/// </summary>
public class Bank
{
    public bool HasSufficientSavings(Customer c, int amount)
    {
        WriteLine($"Check bank for {c.Name}");
        return true;
    }
}

/// <summary>
/// The 'Subsystem ClassB' class
/// </summary>
public class Credit
{
    public bool HasGoodCredit(Customer c)
    {
        WriteLine($"Check credit for {c.Name}");
        return true;
    }
}

/// <summary>
/// The 'Subsystem ClassC' class
/// </summary>
public class Loan
{
    public bool HasNoBadLoans(Customer c)
    {
        WriteLine($"Check loans for {c.Name}");
        return true;
    }
}

/// <summary>
/// The 'Facade' class
/// </summary>
public class Mortgage
{
    private readonly Bank bank = new();
    private readonly Loan loan = new();
    private readonly Credit credit = new();

    public bool IsEligible(Customer cust, int amount)
    {
        WriteLine("{0} applies for {1:C} loan\n",
            cust.Name, amount);

        bool eligible = true;

        // Check creditworthyness of applicant
        if (!bank.HasSufficientSavings(cust, amount))
        {
            eligible = false;
        }
        else if (!loan.HasNoBadLoans(cust))
        {
            eligible = false;
        }
        else if (!credit.HasGoodCredit(cust))
        {
            eligible = false;
        }

        return eligible;
    }
}

/// <summary>
/// Customer class
/// </summary>
public record Customer(string Name);

Output