Builder Design Pattern

The intent of this pattern is to separate construction of an object from its representation, so the same construction process can create different representation.

Its a creational design pattern.
Separates presentation of an object from its construction process.

There are three sections of this pattern:

• Builder: Builder is responsible for defining construction process of each individual part of product. Builder has these small construction processes in it. 
• Director: Director calls concrete builder of product as per client requirement.
• Product: Product is final product that have multiple forms depends on which builder created the product.

Requirement: Whenever we have to create same kind of products with something different representation, we need this pattern.

Use: We can create different products using same construction process.

Problem Solved:  For creating products having different representation, no need to create whole separate process for each.

Sample Code:

    public class ReportDirector

    {

        public ReportDirector()

        {

        }

        public Report CreateReport(ReportBuilder reportBuilder)

        {

            reportBuilder.SetReportType();

            reportBuilder.SetReportTitle();

            reportBuilder.SetReportHeader();

            reportBuilder.SetReportFooter();

            return reportBuilder.GetReport();       

        }

    }

   public abstract class ReportBuilder

    {

        public ReportBuilder()

        {

        }

        public abstract void SetReportType();

        public abstract void SetReportHeader();

        public abstract void SetReportFooter();

        public abstract void SetReportTitle();

        public abstract Report GetReport();

       

    }

    public class ExcelBuilder : ReportBuilder

    {

            Report objExcelReport = new Report();

            public ExcelBuilder()

            {

            }

       

            public override void SetReportType()

            {

                objExcelReport.ReportType = "Excel";

            }

            public override void SetReportHeader()

            {

                objExcelReport.ReportHeader = "Market Survey Report";

            }

            public override void SetReportFooter()

            {

                objExcelReport.ReportFooter = "End of Survey Report";

            }

            public override void SetReportTitle()

            {

                objExcelReport.ReportTitle = "Mediclaim Market Survey";

            }

            public override Report GetReport()

            {

                objExcelReport.Data = "Assign data";

                return objExcelReport;

            }

    }

    public class PDFBuilder : ReportBuilder

    {

        Report objPdfReport = new Report();

        public PDFBuilder()

        {

        }

        public override void SetReportType()

        {

            objPdfReport.ReportType = "PDF";

        }

        public override void SetReportHeader()

        {

            objPdfReport.ReportHeader = "Market Survey Report";

        }

        public override void SetReportFooter()

        {

            objPdfReport.ReportFooter = "End of Survey Report";

        }

        public override void SetReportTitle()

        {

            objPdfReport.ReportTitle = "Mediclaim Market Survey";

        }

        public override Report GetReport()

        {

            objPdfReport.Data = "Assign data";

            return objPdfReport;

        }

    }

    public class Report

    {

        public Report()

        {

        }

        public string ReportType

        {

            get;

            set;

        }

        public string ReportHeader

        {

            get;

            set;

        }

        public string ReportFooter

        {

            get;

            set;

        }

        public string ReportTitle

        {

            get;

            set;

        }

        public string Data

        {

            get;

            set;

        }

    }

Client Code:

        static void Main(string[] args)

        {

            ReportDirector objReportDirector = new ReportDirector();

            ReportBuilder objReportBuilder;

          

            //Generate Excel Report

            objReportBuilder = new ExcelBuilder();

            Report excelReport;

            excelReport = objReportDirector.CreateReport(objReportBuilder);

            Console.WriteLine("Report : " + excelReport.ReportType);

            //Generate PDF Report

            objReportBuilder = new PDFBuilder();

            Report pdfReport;

            pdfReport = objReportDirector.CreateReport(objReportBuilder);

            Console.WriteLine("Report : " + pdfReport.ReportType);

            Console.ReadLine();

        }

    }

In .Net core below given is the example of builder pattern that we have in Program.cs 

var builder = WebApplication.CreateBuilder(args);

 // Add services to the container.

builder.Services.AddControllers();
builder.Services.AddRazorPages(); 
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddResponseCompression();
builder.Services.AddResponseCaching();
builder.Services.AddOutputCache();
var app = builder.Build();