Dependency Injection

Dependency Injection (DI) pattern สำหรับ loose coupling, testability และ flexibility

ทำความเข้าใจ DI

print("Dependency Injection Concepts:")
print("=" * 50)

print("""
Without DI (tightly coupled):
   class OrderService:
       def __init__(self):
           self.db = PostgresDB()  # Hardcoded dependency
           self.mailer = SmtpMailer()  # Hardcoded

       def create_order(self, data):
           self.db.save(data)
           self.mailer.send("Order created")

Problems:
   - Can't use different database
   - Hard to test (need real DB)
   - OrderService knows too much

With DI (loosely coupled):
   class OrderService:
       def __init__(self, db, mailer):  # Dependencies injected
           self.db = db
           self.mailer = mailer

       def create_order(self, data):
           self.db.save(data)
           self.mailer.send("Order created")

Benefits:
   - Easy to swap implementations
   - Easy to test with mocks
   - OrderService only knows interfaces
""")