SQLite Database — Gotchas & Best Practices

For full service implementation, constants, data model templates, and common patterns, see references/sqlite-database-api.md.

⚠️ Wrong Package Trap

<!-- ❌ WRONG — these are different libraries with incompatible APIs -->
<PackageReference Include="Microsoft.Data.Sqlite" />
<PackageReference Include="sqlite-net" />
<PackageReference Include="SQLitePCL.raw" />

<!-- ✅ CORRECT — sqlite-net-pcl by praeclarum + its bundle -->
<PackageReference Include="sqlite-net-pcl" Version="1.9.*" />
<PackageReference Include="SQLitePCLRaw.bundle_green" Version="2.1.*" />

Common Mistakes

❌ Using Environment.GetFolderPath for Database Path

// ❌ Not cross-platform safe — fails on some MAUI targets
var path = Path.Combine(Environment.GetFolderPath(
    Environment.SpecialFolder.LocalApplicationData), "app.db3");

// ✅ Use FileSystem.AppDataDirectory for all MAUI platforms
var path = Path.Combine(FileSystem.AppDataDirectory, "app.db3");

❌ 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

| Platform | Pitfall | |----------|---------| | iOS | FileSystem.AppDataDirectory is iCloud-backed — use FileSystem.CacheDirectory to exclude DB from iCloud backup | | All | Multiple SQLiteAsyncConnection instances to same file → data corruption | | All | No WAL → readers block writers, poor concurrent performance | | All | File operations on open DB → corruption |

Decision Framework

| Question | Recommendation | |----------|---------------| | DI lifetime? | Singleton — one connection, WAL handles concurrent reads | | WAL mode? | Always enable — no reason not to on mobile | | Database path? | FileSystem.AppDataDirectory — never Environment.GetFolderPath | | Save pattern? | Check Id != 0 → Update, else Insert | | Multiple tables? | Add all CreateTableAsync<T>() calls in lazy init | | Need to export/backup? | Close connection first, then File.Copy |

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