sqflite_platform_interface: writing a platform implementation

package:sqflite_platform_interface is the common interface of the sqflite federated plugin. sqflite (the app-facing package) declares sqflite_android and sqflite_darwin as default implementations; both are SqflitePlatform subclasses whose registerWith() installs the method channel DatabaseFactory as the global databaseFactory of package:sqflite_common. Depend on this package only from an implementation package; apps depend on sqflite.

import 'package:sqflite_platform_interface/sqflite_platform_interface.dart';

/// Referenced as `dartPluginClass` in pubspec.yaml.
class SqfliteMyPlatform extends SqflitePlatform {
  static void registerWith() {
    // Native side speaks the com.tekartik.sqflite method channel protocol.
    SqflitePlatform.initWithDatabaseFactoryMethodChannel();
  }
}

Guidelines

• Extend SqflitePlatform (it extends PlatformInterface with a private token; implements is rejected by PlatformInterface.verify).
• Expose a static registerWith() and declare it in the implementation package pubspec.yaml under flutter: plugin: platforms: <platform>: dartPluginClass: <Class>, together with pluginClass (and package on Android) for the native side. Flutter calls it before main().
• If your native code implements the sqflite method channel protocol (channel com.tekartik.sqflite, methods openDatabase, closeDatabase, query, queryCursorNext, insert, update, execute, batch, getDatabasesPath, databaseExists, deleteDatabase, readDatabaseBytes, writeDatabaseBytes, options, debug), call SqflitePlatform.initWithDatabaseFactoryMethodChannel() from registerWith(). It sets databaseFactoryOrNull ??= SqflitePlatform.databaseFactoryMethodChannel, so an already registered factory is kept. The wire format is described in sqflite_common/doc/method_call_protocol.md.
• If the implementation is a Dart-side DatabaseFactory (ffi, web, in-memory), assign it with SqflitePlatform().databaseFactory = factory or directly databaseFactory = factory from package:sqflite_common/sqflite.dart. The factory must be a real sqflite implementation: build it with the SqfliteDatabaseFactoryMixin / buildDatabaseFactory(invokeMethod: ...) helpers that sqflite_common exports for implementers (package:sqflite_common/src/mixin/import_mixin.dart, an implementation import) so that openDatabase, versioning, transactions and batches reuse the shared Dart logic. A plain class implementing DatabaseFactory is rejected by the setter.
• SqflitePlatform().databaseFactory (instance getter) returns the current global factory; SqflitePlatform.databaseFactoryMethodChannel returns the method channel one.
• Errors: the method channel factory converts a PlatformException whose code is sqlite_error into a DatabaseException; native code must use that code and pass the SQL and arguments in details so DatabaseException.toString() and getResultCode() work.
• Keep the package Flutter-only concerns (channels, registerWith) here; put anything reusable in sqflite_common.

Examples

pubspec.yaml of an implementation package

name: sqflite_myos
dependencies:
  flutter:
    sdk: flutter
  sqflite_platform_interface: ">=2.4.1 <4.0.0"
  sqflite_common: ">=2.5.9 <4.0.0"

flutter:
  plugin:
    implements: sqflite
    platforms:
      myos:
        pluginClass: SqflitePlugin
        dartPluginClass: SqfliteMyOs

Method channel implementation

import 'package:sqflite_platform_interface/sqflite_platform_interface.dart';

class SqfliteMyOs extends SqflitePlatform {
  /// Called by Flutter at startup (dartPluginClass).
  static void registerWith() {
    SqflitePlatform.initWithDatabaseFactoryMethodChannel();
  }
}

Registering a Dart-side factory

import 'package:sqflite_common/sqlite_api.dart';
import 'package:sqflite_platform_interface/sqflite_platform_interface.dart';

/// [factory] must come from an sqflite implementation (for example
/// databaseFactoryFfi from sqflite_common_ffi, or one built with
/// buildDatabaseFactory).
void registerDartFactory(DatabaseFactory factory) {
  SqflitePlatform().databaseFactory = factory;
}

Reading the factory from the interface

import 'package:sqflite_common/sqlite_api.dart';
import 'package:sqflite_platform_interface/sqflite_platform_interface.dart';

Future<Database> openThroughInterface(String path) {
  final DatabaseFactory factory = SqflitePlatform().databaseFactory;
  return factory.openDatabase(path);
}

Common mistakes

• Depending on sqflite_platform_interface from an application; apps use package:sqflite (or sqflite_common + an implementation).
• Forgetting dartPluginClass in the pubspec, so registerWith() never runs and openDatabase throws StateError: databaseFactory not initialized.
• Assigning a custom class that merely implements DatabaseFactory: ArgumentError: Unsupported sqflite factory.
• Returning errors with a code other than sqlite_error from native code; they surface as raw PlatformExceptions instead of DatabaseException.

More

Default implementations to copy from: sqflite_android (Kotlin/Java, SqfliteAndroid) and sqflite_darwin (Objective-C, SqfliteDarwin, sharedDarwinSource). App-level usage: the sqflite package skills.