Association, Aggregation, Composition

No worries Maham — you're not alone! This confusion is super common. Let's break it without any textbook stuff, only using bank examples and your way of understanding 👇

🎯 First, remember this:

All 3 — Association, Aggregation, Composition — are ways of connecting classes.

🧠 Let's say we have:

A Customer
A Bank
An Account

✅ Association → Just “friendship”

Class A uses Class B
No ownership, no storing inside
Just passes object when needed

class Customer:
    def __init__(self, name):
        self.name = name

class Bank:
    def serve_customer(self, customer):
        print(f"Hello {customer.name}, how can I help?")

🪄 Explanation:

Bank is not storing the customer
Customer is passed just during the method
No ownership, just using

✅ Aggregation → “Has a”, but loose ownership

One class stores another object
But object is created outside
So, they can live independently

class Account:
    def __init__(self, number):
        self.number = number

class Customer:
    def __init__(self, name, account):
        self.name = name
        self.account = account

acc = Account("12345")
cust = Customer("Maham", acc)

🪄 Explanation:

Customer stores an account object
But account was made outside first
If you delete customer, account can still be reused

✅ Composition → Strong ownership (like marriage)

One class creates and owns another
Created inside constructor
Life of both are tied

class Customer:
    def __init__(self, name):
        self.name = name
        self.account = Account("12345")  # Created inside

🪄 Explanation:

Customer created its own account inside
You don’t pass it from outside
If you delete customer, account is also gone

🔁 Summary again (in Maham style):

Relationship	Created Where?	Stored Inside?	Life Tied?	Ownership
Association	Outside	❌	❌	❌
Aggregation	Outside	✅	❌	🟡 Weak
Composition	Inside	✅	✅	✅ Strong

Simple Definitions (Bank style):

Association → Just a “temporary guest”
→ Pass the object in a method, not stored
→ No strong connection
Aggregation → A “flatmate”
→ You store the object by passing it in the constructor
→ But both can live separately
Composition → A “spouse”
→ You create the object inside the constructor
→ Their life is tied with your class