What is stored in the data layer?

The Data Layer stores the following information:

• Data sources: Implementations of data sources such as:

  • Local databases (Room, SQLite).
  • Client APIs for interacting with network services (Retrofit, Volley).
  • File storage.
  • SharedPreferences.

• Repositories: Interfaces and implementations of repositories that provide unified access to various data sources. The repository abstracts the data source layer from the business logic.

• Data models: Classes representing the structure of data obtained from data sources (e.g., POJO, Data Classes). These models are usually different from those used in the presentation layer.

• Mappers: Functions or classes for transforming data models from one format to another, for example, from a network response format to a format used by the repository.

• Data-related logic: Business logic specific to working with data, such as caching, error handling during API requests, database migrations.

The main goal of the data layer is to be the single source of truth for data in the application, hiding the details of data retrieval from upper layers.