Entity (DDD series part 7)

Krzysztof Słomka
3 min readJan 17, 2023
Photo by Jess Bailey on Unsplash

In Domain-Driven Design (DDD), the concept of an Entity is used to represent the key concepts of the business domain.

An Entity is an object that has a unique identity and an associated set of attributes and behaviors. In this post, we will explore what an Entity is, why it’s important, and how it can be used to improve the design of software systems.

An Entity is an object that represents a unique thing in the business domain. It has a unique identity, which is used to distinguish it from other objects in the system. Additionally, an Entity has an associated set of attributes, which describe its state, and behaviors, which describe its actions.

One of the key benefits of using Entities is that they help to create a clear separation between the business domain and the implementation of the system. By modeling the key concepts of the business domain as Entities, we can ensure that the system is closely aligned with the business domain and that it meets the needs of the business.

Example

Let’s consider an example of an e-commerce application. In this application, we have several key concepts such as Product, Order, and Customer. Each of these concepts can be modeled as an Entity.

The Product Entity

Would have a unique identifier, such as a product code, and an associated set of attributes, such as name, price, and description. It would also have behaviors, such as methods for calculating the total cost of an order or for updating the stock level.

The Order Entity

Would also have a unique identifier, such as an order number, and an associated set of attributes, such as customer, products, and total cost. It would also have behaviors, such as methods for calculating the total cost of an order or for adding or removing products from an order.

The Customer Entity

Would also have a unique identifier, such as an email address, and an associated set of attributes, such as name, address, and phone number. It would also have behaviors, such as methods for updating a customer’s address or for adding or removing a shipping address.

Entities can also have relationships with other Entities. For example, the Order Entity would have a relationship with the Product and Customer Entities, because an order is related to both a product and a customer.

In conclusion, Entities are a powerful tool for modeling the key concepts of the business domain in Domain-Driven Design. They help to create a clear separation between the business domain and the implementation of the system and ensure that the system is closely aligned with the business domain. By modeling key concepts as Entities

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Krzysztof Słomka

My name is Krzysztof, I'm a software architect and developer, with experience of leading teams and delivering large scalable projects for over 13 years...