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في هذا الدرس

explain why we split code into layers.

الموضوعات المخطط لها

• One class doing HTTP, rules, and data access is hard to read, test, and change.
• Each layer has one job and talks only to the layer below.
• Flow: controller → service → repository; the domain model is shared by service and repository.
• Layers let you change one part (say, the database) without rewriting the rest.