Template Method Pattern in C# – Real-Time Example (Algorithm Skeleton)

What is Template Method Pattern?

The Template Method Pattern is a behavioral design pattern that defines the overall structure (template) of an algorithm in a base class, while allowing subclasses to implement specific steps.

👉 Common workflow stays fixed

👉 Individual steps can vary

Why Use Template Method Pattern?

  • Reuse common workflow logic
  • Avoid duplicate code
  • Standardize process flow
  • Allow customizable steps
  • Improve maintainability

Real-Time Scenario

Report Generation:

  • Fetch data
  • Format report
  • Export report

Different report types:

  • PDF Report
  • Excel Report

👉 Workflow is same, implementation differs.

Real-Time Example – Report Generation System

Step 1: Abstract Base Class


public abstract class ReportGenerator
{
    // Template Method
    public void GenerateReport()
    {
        GetData();
        FormatReport();
        ExportReport();
    }

    protected abstract void GetData();
    protected abstract void FormatReport();
    protected abstract void ExportReport();
}

Step 2: Concrete Implementation – PDF Report


public class PdfReportGenerator : ReportGenerator
{
    protected override void GetData()
    {
        Console.WriteLine("Fetching PDF Data");
    }

    protected override void FormatReport()
    {
        Console.WriteLine("Formatting PDF Report");
    }

    protected override void ExportReport()
    {
        Console.WriteLine("Exporting PDF Report");
    }
}

Step 3: Concrete Implementation – Excel Report


public class ExcelReportGenerator : ReportGenerator
{
    protected override void GetData()
    {
        Console.WriteLine("Fetching Excel Data");
    }

    protected override void FormatReport()
    {
        Console.WriteLine("Formatting Excel Report");
    }

    protected override void ExportReport()
    {
        Console.WriteLine("Exporting Excel Report");
    }
}

Usage Example


ReportGenerator report =
    new PdfReportGenerator();

report.GenerateReport();

Output


Fetching PDF Data
Formatting PDF Report
Exporting PDF Report

Key Concept

Instead of:


CreatePdfReport();
CreateExcelReport();

With duplicated workflow ❌

We define:


GenerateReport()

👉 Common structure reused.

Diagram Understanding


ReportGenerator
      ↓
-------------------------
PdfReportGenerator
ExcelReportGenerator

👉 Base class controls algorithm flow.

Advantages

  • ✔ Reuse common logic
  • ✔ Reduces duplicate code
  • ✔ Standardized workflow
  • ✔ Easy to extend
  • ✔ Better maintainability

Disadvantages

  • ✖ Inheritance-based design
  • ✖ Less flexible than composition
  • ✖ Changes in base class affect subclasses

When to Use

Use Template Method when:

  • Multiple processes share same workflow
  • Only some steps vary
  • Standardized process flow is needed
  • Duplicate algorithm structure exists

Real Project Mapping (.NET + Angular)

Feature Usage
Report generation Template Method
File export systems Template Method
ETL/Data processing Template Method
Payment workflow Template Method
Email templates Template Method

ASP.NET Core Real Example

Controller Lifecycle


Request
   ↓
Authentication
   ↓
Authorization
   ↓
Action Execution
   ↓
Response

👉 Framework defines template flow.

Advanced Example – Payment Processing


ProcessPayment()
   ↓
Validate
   ↓
Calculate Charges
   ↓
Complete Transaction

👉 Different payment providers override specific steps.

Template Method vs Strategy

Template Method Strategy
Uses inheritance Uses composition
Workflow fixed in base class Behavior interchangeable
Algorithm structure controlled Algorithms fully replaceable

Pro Tip

Template Method works well with:

  • Base service classes
  • Report engines
  • Workflow systems
  • ETL pipelines
  • Framework development

Summary

Template Method helps you:

  • Define reusable workflows
  • Avoid duplicate logic
  • Standardize algorithms

👉 Perfect for:

  • Report systems
  • Export pipelines
  • Workflow engines
  • Reusable business processes

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