SQLite Database — Gotchas & Best Practices

❌ Multiple SQLiteAsyncConnection Instances

SQLiteAsyncConnection is not thread-safe for multiple instances pointing at the same file. Use a single instance via DI singleton:

// ❌ Creating new connections per request
public async Task<List<Item>> GetItems()
{
    var db = new SQLiteAsyncConnection(Constants.DatabasePath);
    return await db.Table<Item>().ToListAsync();
}

// ✅ Lazy singleton — one connection, created once
private SQLiteAsyncConnection? _database;
private async Task<SQLiteAsyncConnection> GetDatabaseAsync()
{
    if (_database is not null) return _database;
    _database = new SQLiteAsyncConnection(Constants.DatabasePath, Constants.Flags);
    await _database.ExecuteAsync("PRAGMA journal_mode=WAL;");
    await _database.CreateTableAsync<TodoItem>();
    return _database;
}

❌ Forgetting WAL Mode

Without WAL, readers block writers. Always enable it at initialization:

await _database.ExecuteAsync("PRAGMA journal_mode=WAL;");

❌ File Operations on Open Database

// ❌ Moving/deleting while connection is open — data corruption
File.Delete(Constants.DatabasePath);

// ✅ Always close first
await databaseService.CloseConnectionAsync();
if (File.Exists(Constants.DatabasePath))
    File.Delete(Constants.DatabasePath);

Platform Pitfalls

Decision Framework

Performance Tips

1. Use transactions for batch writes — individual inserts are slow; wrap in RunInTransactionAsync
2. Add [Indexed] to frequently queried columns — especially foreign keys
3. WAL mode eliminates reader/writer contention
4. Avoid ToListAsync() on large tables — use Where() filtering and pagination
5. Use raw SQL for complex queries — QueryAsync<T> is faster than chained LINQ for joins

Checklist

• Install sqlite-net-pcl + SQLitePCLRaw.bundle_green (not Microsoft.Data.Sqlite)
• Database path uses FileSystem.AppDataDirectory
• Models have [PrimaryKey, AutoIncrement]
• Single DatabaseService with lazy async init pattern
• WAL enabled via PRAGMA journal_mode=WAL
• DatabaseService registered as singleton in DI
• Connection closed before any file move/copy/delete
• iOS: DB excluded from iCloud backup if needed