Inheritance Mappers Design Pattern

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What is the Inheritance Mappers Design Pattern?

The Inheritance Mappers design pattern belongs to the Object-Relational Structural Patterns category in Enterprise Application Architecture.

Its primary purpose is to provide a structured way to organize database mappers that handle complex class inheritance hierarchies when transferring data between domain objects and relational database tables.

How Inheritance Mappers Work

In Object-Relational Mapping (ORM), mapping an inheritance hierarchy can follow strategies such as:

• Single Table Inheritance: One table stores all classes in the hierarchy.
• Class Table Inheritance: Each class in the hierarchy has its own corresponding table.
• Concrete Table Inheritance: Only concrete classes have database tables.

Practical Hierarchy Example: Player Domain Model

Consider an inheritance structure:

• Player (Superclass with name attribute)
• Footballer extends Player (adds club attribute)
• Cricketer extends Player (adds battingAverage attribute)
• Bowler extends Cricketer (adds bowlingAverage attribute)

Using dedicated mappers (e.g., PlayerMapper, FootballerMapper, CricketerMapper, BowlerMapper), each mapper is responsible for:

• Extracting values from domain objects and persisting them into appropriate database tables.
• Reading rows from tables and reconstructing the corresponding domain objects (CRUD operations).

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Inheritance Mappers Design Pattern