Data Layer API

SQLite persistence with versioned schema migrations and parameterized queries.

LocalStorage

lib/data/local_storage.dart

Singleton SQLite database manager using sqflite. Provides a shared Database instance with lazy initialization.

Database Schema (v4)

users

Column	Type	Constraint
`id`	TEXT	PRIMARY KEY
`name`	TEXT	—
`email`	TEXT	—

events

Column	Type	Default	Added in
`id`	TEXT	PRIMARY KEY	v1
`title`	TEXT	—	v1
`description`	TEXT	`''`	v2
`date`	TEXT	—	v1
`priority`	TEXT	`'medium'`	v2
`tags`	TEXT	`'[]'`	v3
`recurrence`	TEXT	`null`	v4

Schema Migrations Migrations run incrementally via onUpgrade. Each version check is independent — upgrading from v1→v4 runs all three ALTER TABLE statements. This ensures any prior version upgrades correctly.

Static Methods

Method	Signature	Description
`database`	`Future<Database>` (getter)	Returns cached DB instance; creates on first access
`insert`	`(String table, Map data) → Future<void>`	Insert/upsert row with `ConflictAlgorithm.replace`
`getAll`	`(String table) → Future<List<Map>>`	Query all rows from a table
`delete`	`(String table, String id) → Future<void>`	Delete row by ID (parameterized query)
`close`	`() → Future<void>`	Close DB connection and clear cache. Next access re-opens.

SQL Injection Prevention All queries use parameterized whereArgs — never string interpolation. The delete method uses where: 'id = ?', whereArgs: [id].

EventRepository

lib/data/repositories/event_repository.dart

Thin wrapper around LocalStorage providing domain-specific event operations.

Methods

Method	Signature	Description
`getEvents()`	`Future<List<Map>>`	Fetch all events from the `events` table
`saveEvent(json)`	`Future<void>`	Insert/upsert an event
`updateEvent(json)`	`Future<void>`	Update an existing event (uses upsert)
`deleteEvent(id)`	`Future<void>`	Delete event by ID

UserRepository

lib/data/repositories/user_repository.dart

Persists user profiles for session restoration.

Methods

Method	Signature	Description
`saveUser(json)`	`Future<void>`	Persist user profile
`getUser(id)`	`Future<Map?>`	Retrieve user by ID

Persistence Flow

Widget Action
  │
  ▼
EventService
  ├─→ EventProvider.addEvent()     ← instant UI update
  └─→ EventRepository.saveEvent() ← async disk write
        └─→ LocalStorage.insert('events', json)
              └─→ sqflite INSERT OR REPLACE

Why This Pattern?

Responsiveness — UI updates instantly (in-memory first)
Resilience — Disk failures don't crash the app
Consistency — Single service coordinates both stores
Testability — Repository can be mocked in EventService tests