flutter-working-with-databases

Architecting the Data Layer

Contents

• Core Architecture
• Services Implementation
• Repository Implementation
• Caching Strategies
• Workflows
• Examples

Core Architecture

Construct the data layer as the Single Source of Truth (SSOT) for all application data. In an MVVM architecture, the data layer represents the Model. Never update application data outside of this layer.

Separate the data layer into two distinct components: Repositories and Services.

Repositories

• Act as the SSOT for a specific domain entity.
• Contain business logic for data mutation, polling, caching, and offline synchronization.
• Transform raw data models (API/DB models) into Domain Models (clean data classes containing only what the UI needs).
• Inject Services as private members to prevent the UI layer from bypassing the repository.

Services

• Act as stateless wrappers around external data sources (HTTP clients, SQLite databases, platform plugins).
• Perform no business logic or data transformation beyond basic JSON serialization.
• Return raw data models or Result wrappers to the calling repository.

Services Implementation

Database Services (SQLite)

Use databases to persist and query large amounts of structured data locally.

• Add sqflite and path packages to pubspec.yaml.
• Use the path package to define the storage location on disk safely across platforms.
• Define table schemas using constants to prevent typos.
• Use id as the primary key with AUTOINCREMENT to improve query and update times.
• Always use whereArgs in SQL queries to prevent SQL injection (e.g., where: 'id = ?', whereArgs: [id]).

API Services

• Wrap HTTP calls (e.g., using the http package) in dedicated client classes.
• Return asynchronous response objects (Future or Stream).
• Handle raw JSON serialization at this level, returning API-specific data models.