Domain Model Design Pattern - Samples

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What is the Domain Model Design Pattern?

The Domain Model Pattern is an object-oriented approach to structuring enterprise business logic, popularized by Martin Fowler in Patterns of Enterprise Application Architecture (PofEAA).

Instead of separating data structures from business rules, a Domain Model combines both data and behavior into interconnected domain objects. Depending on complexity, domain models generally fall into two categories: Simple Domain Model and Rich Domain Model.

1. Simple Domain Model (Table-to-Class Mapping)

In a Simple Domain Model, your domain classes closely mirror your database tables. Each table typically corresponds directly to a single domain entity class:

• Player Table: Maps directly to a Player domain class.
• Footballer Table: Maps directly to a Footballer domain class.
• Cricketer Table: Maps directly to a Cricketer domain class.
• Bowler Table: Maps directly to a Bowler domain class.

This 1-to-1 mapping works best when your relational database design is clean and your domain rules align directly with standard database structures.

2. Rich Domain Model (Object-Oriented Abstraction)

A Rich Domain Model uses true object-oriented concepts like inheritance, polymorphism, and encapsulation. The object hierarchy does not have to match the underlying database tables directly:

• Complex Logic: Contains rich behaviors and business calculation methods right inside the entity classes.
• Flexible Schema: For instance, a single Employee database table can be abstracted into multiple domain classes (such as FullTimeEmployee and ContractorEmployee) through inheritance.
• Enterprise Ready: Ideal for complex business systems with ever-evolving rules and validation flows.

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Recommended Design Pattern Tutorials:

• Composite Design Pattern: Class Diagram Explained
• Prototype Design Pattern Explained: Introduction and Fundamentals
• Registry Design Pattern Demystified

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Domain Model Design Pattern - Samples