Builder Pattern

Construct complex objects step by step with flexible configuration

Pattern Overview

🏗️ The Builder Pattern - Complex Object Construction

Constructs complex objects step by step, allowing different representations of the same construction process. Perfect for creating objects with many optional parameters!

Core Problem Solved:
Avoid telescoping constructor parameters
Create objects with complex initialization
Support different representations of same object
Enable step-by-step construction process

🔍 Three Implementation Approaches:

Method Chaining: Fluent interface with returning 'this'
Director Pattern: Separate builder from construction logic
Functional Builder: Immutable approach with function composition
Real-World Applications:
SQL query builders and ORM query construction
HTTP request builders in API clients
Configuration objects for complex systems
Test data builders in testing frameworks
UI component builders and form generators
Document and report generators
Modern Usage Examples:
React component prop builders
GraphQL query builders
Docker container configuration
Webpack configuration builders

Examples:

SQL query construction

Input:

QueryBuilder().select(['name', 'email']).from('users').where('active = 1')

Output:

SELECT name, email FROM users WHERE active = 1

House construction

Input:

HouseDirector.buildLuxuryHouse(new ModernHouseBuilder())

Output:

House with concrete foundation, glass walls, flat roof, garage, and pool

User profile creation

Input:

UserProfileBuilder.create('John', 'john@example.com').withAge(30).withTheme('dark')

Output:

UserProfile with name, email, age 30, and dark theme

Concepts

step-by-step constructionfluent interfaceobject composition

Complexity Analysis

Time:O(n)

Space:O(1)

Implementation

method-chaining

Time: O(n) | Space: O(1)

class QueryBuilder {
  private selectFields: string[] = [];
  private fromTable: string = '';
  private whereConditions: string[] = [];

  public select(fields: string[]): QueryBuilder {
    this.selectFields = [...fields];
    return this; // Enable chaining
  }

  public from(table: string): QueryBuilder {
    this.fromTable = table;
    return this;
  }

  public where(condition: string): QueryBuilder {
    this.whereConditions.push(condition);
    return this;
  }

  public build(): string {
    let query = `SELECT ${this.selectFields.join(', ')} FROM ${this.fromTable}`;
    
    if (this.whereConditions.length > 0) {
      query += ` WHERE ${this.whereConditions.join(' AND ')}`;
    }
    
    return query;
  }
}

// Usage
const query = new QueryBuilder()
  .select(['name', 'email'])
  .from('users')
  .where('active = 1')
  .where('age > 18')
  .build();