Repository

In the previous tutorial, we set up the Notes app architecture with a local database and shared ViewModels. Everything works offline. But real apps need to sync with a server. In this tutorial, we build the shared data layer — adding a Ktor API client, Data Transfer Objects (DTOs), an offline-first sync pattern, and a database migration. All of this code lives in commonMain and runs on both Android and iOS. ...

In the previous tutorial, we planned our task manager app. Now we build the foundation — the data layer. The data layer is everything below the UI: the database, the repository, and the use cases. Get this right, and the UI layer writes itself. What We Build in This Tutorial data/ ├── local/ │ ├── TaskEntity.kt ← Database table definition │ ├── TaskDao.kt ← Database operations │ └── AppDatabase.kt ← Room database ├── mapper/ │ └── TaskMapper.kt ← Convert Entity ↔ Domain Model ├── repository/ │ └── TaskRepositoryImpl.kt ← Repository implementation │ domain/ ├── model/ │ ├── Task.kt ← Clean domain model │ ├── Category.kt ← Enum │ └── Priority.kt ← Enum ├── repository/ │ └── TaskRepository.kt ← Interface (contract) └── usecase/ ├── GetTasksUseCase.kt ├── AddTaskUseCase.kt ├── ToggleTaskUseCase.kt └── DeleteTaskUseCase.kt Step 1: Domain Models The domain layer is pure Kotlin — no Android dependencies, no Room annotations. This is the “truth” of your app. ...