In Part 4 of our CraftIQ.Inventory microservice series, we dive into the design and implementation of the Category module, focusing on RESTful and Specifications design patterns. We begin by explaining the RESTful design pattern, highlighting its principles for creating well-structured and scalable APIs. Additionally, we explore the Specifications design pattern, which allows us to define criteria for querying data in a flexible and reusable manner. To implement these patterns, we create an abstraction for the Category module, defining interfaces for interacting with category data. We then provide a service implementation that leverages these interfaces, enabling us to manage categories effectively. Furthermore, we add endpoints for creating and deleting categories, showcasing how these patterns can be applied in practice to enhance the functionality and maintainability of our microservice. Join us as we continue to refine the CraftIQ.Inventory microservice, incorporating best practices and design patterns to create a robust and efficient API. GitHub Repository: https://github.com/huzcodes/CraftIQ.Inventory