Composition or aggregation?

Composition when the part cannot exist without the whole (an order item without its order is meaningless); aggregation when the part can stand alone (a product exists without any order).

Can a class diagram show the order of method calls?

No, it is a static structure. Use a sequence diagram for call order; the "Microservice call sequence diagram" template is a starting point.

Too many attributes make the diagram tall

Keep only the key attributes and move the full list to a data dictionary, or split the diagram into "customers and orders" and "products and stock".

E-commerce Order System Class Diagram Template

Class diagram with Customer, Order, OrderItem, Product and Payment classes, showing composition, associations and multiplicities. For online shop system design and object-oriented coursework, exported as PNG, Word or PowerPoint for free.

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When to use it

System design documents for shops, object-oriented analysis and design assignments and project reports. Order and OrderItem use composition (filled diamond) because an item cannot exist without its order; Order and Payment are a 0..1 association.

Making it yours

Add Cart, Coupon or Shipment classes as class Name { … } blocks and connect them.
Turn the status into an enumeration: class OrderStatus { <<enumeration>> PENDING PAID SHIPPED }.
Change composition to aggregation by replacing *-- with o--; use a plain --> when unsure.

Mermaid code

classDiagram
    class Customer {
        +String customerId
        +String displayName
        +String phone
        +placeOrder() Order
    }
    class Order {
        +String orderNo
        +Date createdAt
        +String status
        +pay()
        +cancel()
        +total() float
    }
    class OrderItem {
        +int quantity
        +float unitPrice
        +subtotal() float
    }
    class Product {
        +String sku
        +String name
        +float price
        +int stock
        +reduceStock(int)
    }
    class Payment {
        +String transactionId
        +float amount
        +String channel
        +refund()
    }
    Customer "1" --> "*" Order : owns
    Order "1" *-- "1..*" OrderItem : contains
    OrderItem "*" --> "1" Product : refers to
    Order "1" --> "0..1" Payment : settled by

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Draw an e-commerce order system class diagram in Mermaid classDiagram syntax with classes Customer (customerId, displayName, phone; method placeOrder), Order (orderNo, createdAt, status; methods pay, cancel, total), OrderItem (quantity, unitPrice; method subtotal), Product (sku, name, price, stock; method reduceStock), Payment (transactionId, amount, channel; method refund). Customer has many Orders; Order is composed of one or more OrderItems; OrderItem refers to one Product; Order is settled by zero or one Payment. Output only the mermaid code block.

FAQ

Composition or aggregation?: Composition when the part cannot exist without the whole (an order item without its order is meaningless); aggregation when the part can stand alone (a product exists without any order).
Can a class diagram show the order of method calls?: No, it is a static structure. Use a sequence diagram for call order; the "Microservice call sequence diagram" template is a starting point.
Too many attributes make the diagram tall: Keep only the key attributes and move the full list to a data dictionary, or split the diagram into "customers and orders" and "products and stock".

E-commerce Order System Class Diagram Template

When to use it

Making it yours

Mermaid code

Ask an AI for one with this structure

FAQ

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