The decorator pattern is one of the most versatile design patterns available to us in software engineering. It allows for behaviour to be added to an object dynamically while still obeying the Single Responsibility Principle. It is similar to the Chain of Responsibility pattern, which I wrote about here, but a key difference is that instead of a single class (or link in the chain) handling a particular request or action, all classes handle the request or action.
This article shows how useful this can be when transforming data, typically as part of an Extract, Transform, and Load pipeline. In the example, we’ll see how the decorator pattern can be applied to extend the functionality of an object all while maintaining compliance with the Single Responsibility Principle.
Ok — let’s crack on.
In this example imagine a system that stores and processes commodity data — data about oil, gold, silver, etc. Specifically, we’ll be looking at a Data Transfer Object, a DTO, that holds data retrieved from the database.

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