Entities

It can be difficult to model a domain. Once the whole model is done, the next step is to move on to the code. The best approach to translate the domain model into code is to use Object-Oriented Programming (OOP). To implement this approach, DDD defines a number of artifacts that allow technical experts to represent a domain model in the code.

What is Model Driven Design?

Model Driven Design (MDD) says that a software solution should be implemented based on the analysis of models. Remember that a model is an abstraction and representation of something from the real world that makes it easy for us to understand it. Once a domain is modeled, it is possible to begin the implementation of software.

Beyond the MDD methodology, the Object Management Group (OMG) created a conceptual framework called Model Driven Architecture (MDA). The MDA approach provides guidelines for how to structure software specifications that are expressed as models. It covers the complete development lifecycle in the analysis, design, programming, testing, deployments, and maintenance stages. MDA uses three models:

1. Computation Independent Model (CIM): This model focuses on the domain model.
2. Platform Independent Model (PIM): This model focuses on a general platform, where a solution is deployed.
3. Platform Specific Model (PSM): This model focuses on a specific platform, where a solution is deployed.

What is an entity in the DDD world?

According to Model Driven Design, DDD uses tactical patterns to represent a model. There are three possible domain objects for the implementation of business logic: entities, value objects, and aggregates.

In the context of DDD, an entity represents something that is involved in a business process. For example, in the context of a bank, some entities may be Account, Credit Card, Customer, or Transaction. An entity shows well-defined attributes and domain behavior. Additionally, it is identified by a form of identification, such as an ID or a key, which implies that attribute values may change when required. This is why this domain object is mutable. The identification of an object is not affected when attribute values change.