Applying ER Model Concepts
In the previous cheatsheet, we have understood the core concepts of ER Model — entity types, relationships and attributes. Now, let's build an ER model for a real-world scenario.
E-commerce Application
In a typical e-commerce application,
- Customer has only one cart. A cart belongs to only one customer
- Customer can add products to cart
- Cart contains multiple products
- Customer can save multiple addresses in the application for further use like selecting delivery address
Let’s apply the concepts of ER Model to this e-commerce scenario.
Entity types
- Customer
- Product
- Cart
- Address
Relationships
Let's understand the relationships in the e-commerce use-case.
Relation Between Cart and Customer
- A customer has only one cart.
- A cart is related to only one customer.
- Hence, the relation between customer and cart entities is One-to-One relation.
Relation Between Cart and Products
- A cart can have many products.
- A product can be in many carts.
- Therefore, the relation between cart and product is Many-to-Many relation.
Relation Between Customer and Address
- A customer can have multiple addresses.
- An address is related to only one customer.
- Hence, the relation between customer and address is One-to-Many relation.
Attributes
Following are the attributes for the entity types in the e-commerce scenario. Here, attributes like id, product_id, etc., are key attributes as they uniquely identify each entity in the entity type.
ER Model of e-commerce application
